Credit score

First of all, how much did your credit score do down? If it is somewhat minimal, then you can generally ignore that as minor fluctuations are normal.

Further, did you review your credit reports? You can get all of them, free of charge, from the site below and, if necessary, dispute any inaccuracies.

https://www.annualcreditreport.com/index.action

if you have credit cards, it is very like your credit score will change from period to period. 

here's sometime from FICO

Understanding FICO® Scores
What are FICO® Scores?
FICO® Scores are the most widely used credit scores. Each FICO® Score is a three-digit number calculated from the data on your credit reports at the three major consumer reporting agencies—Experian, TransUnion and Equifax. Your FICO® Scores predict how likely you are to pay back a credit obligation as agreed. Lenders use FICO® Scores to help them quickly, consistently and objectively evaluate potential borrowers’ credit risk.
What goes into FICO® Scores?
FICO® Scores are calculated from the credit data in your credit report. This data is grouped into five categories; the chart below shows the relative importance of each category.
1.
35% - Payment history:
Whether you've paid past credit accounts on time
2.
30% - Amounts owed:
The amount of credit and loans you are using
3.
15% - Length of credit history:
How long you've had credit
4.
10% - New credit:
Frequency of credit inquires and new account openings
5.
10% - Credit mix:
The mix of your credit, retail accounts, installment loans, finance company accounts and mortgage loans
What are score factors?
Score factors are delivered with a consumer’s FICO® Score, these are the top areas that affected that consumer’s FICO® Scores. The order in which the score factors are listed is important. The first factor indicates the area that most affected the score and the second factor is the next most significant influence. Addressing these factors can benefit the score.
Why is my FICO® Score different than other scores I’ve seen?
There are many different credit scores available to consumers and lenders. FICO® Scores are the credit scores used by most lenders, and different lenders may use different versions of FICO® Scores. In addition, FICO® Scores are based on credit file data from a consumer reporting agency, so differences in your credit files may create differences in your FICO® Scores.
Why do FICO® Scores fluctuate/change?
There are many reasons why a score may change. FICO® Scores are calculated each time they are requested, taking into consideration the information that is in your credit file from a consumer reporting agency at that time. So, as the information in your credit file at that CRA changes, FICO® Scores can also change. Review your key score factors, which explain what factors from your credit report most affected a score. Comparing key score factors from the two different time periods can help identify causes for a change in a FICO® Score. Keep in mind that certain events such as late payments or bankruptcy can lower FICO® Scores quickly.
How do I check my credit report for free?
You may get a free copy of your credit report from each of the three major consumer reporting agencies annually. To request a copy of your credit report, please visit: www.annualcreditreport.com. Please note that your free credit report will not include your FICO® Score. Because your FICO® Score is based on the information in your credit report, it is important to make sure that the credit report information is accurate.
Will receiving my FICO® Score impact my credit?
No. The FICO® Score we provide to you will not impact your credit.

here are other things that could affect your score

Derogatory marks
Derogatory marks are good to avoid — they can stay on your report for 7-10 years.
If you have a collection
1. Since debt collectors need to have proof that their info is accurate, you should dispute a collection if anything’s off.
2. Know your rights — debt collectors can’t keep calling you.
3. See if it’s worth negotiating your debt. If it’s old, you might just wait for it to fall off.
If you have a public record
1. Public records like bankruptcies, civil judgements, and tax liens are harder to remove.
2. If any info is wrong, get documentation and court records to build your case.
3. Dispute with the credit bureaus to remove the public record.
Credit age
Lenders typically like to see that you have experience using credit responsibly.
What to know
1. If you’re paring down your accounts, don’t close your oldest credit card — it’s what gives you a long credit history
2. Sometimes credit cards will close an old account that never gets used. Use an old card now and then to prevent a potential score drop.
3. When an older account (like mortgage or student loan) falls off your report, your score could drop since you’re losing the credit history that comes with that account.

There's a limited number of accounts on your report
Lenders typically like to see that you've used a variety of accounts responsibly.
What to know
1. Having different account types (like credit cards and loans) can help your credit.
2. Don’t fret about an exact number or mix, since you’ll build these over time. The important thing is that you’re using accounts responsibly.
3. If a mortgage, student loan or auto loan falls off your report, your score could drop since you’re losing a line of credit that’s given you a lot of credit
4. NOT SHOWN BUT IT WOULD APPEAR THAT HAVING 7 TO 21+ ACCOUNTS IS BETTER THAN HAVING 0 TO 6

Hard inquiries
Hard inquiries from things like credit applications can stay on your report for up to 2 years, but their effects tend to fade over time.
What to know
1. Good news! It’s a temporary ding and scores usually bounce back in 3 months.
2. Plan ahead and minimize your hard inquiries at least 9-12 months before trying to get a mortgage or big loan.