Why I couldn’t file head of house hold?

No one can see your information, so we do not know why you could not file as Head of Household.  Did you claim a qualified dependent?   The dependent cannot be a GF or BF.  The dependent must be related to you.

Am I Head of Household?

https://ttlc.intuit.com/questions/1894553-do-i-qualify-for-head-of-household

https://ttlc.intuit.com/questions/2900097-what-is-a-qualifying-person-for-head-of-household

If you qualify as Head of Household, when you enter your marital status (single or married filing separately) into MyInfo, and then enter your qualifying dependent, TurboTax will offer HOH as your filing status.

Why do you think you should be able to File HoH?

There are a few of  common situation where you are not:

1. The person you claim as a dependent is not closely related (e.g. girlfriend)

2. You are the non custodial parent claiming the child as a dependent (the child doesn't live with you enough time)

3. The related dependent lived with you less than half the year