I always claim myself and now my mom thinks she can claim me even though I have proof of paying my own rent and being a roommate to her

you would be her dependent (qualifying child) if all these tests are met

1) Same principal abode as mom for more than ½ the tax year. Temporary absences like for school are ignored
2) If not a full-time student, under 19 at the end of the tax year. If a full-time student under 24 at end of tax year.
3 Hasn’t provided over ½ your own support  (who pays for everything else besides rent)

if you are not a qualifying child you could be a quallifying relative (her dependent) if these test are met

1) your gross income for 2019 is less than $4,200
2) mom provides over ½ your support
3) you aren't a qualifying child of another taxpayer

these tests have been in effect for years, so perhaps you wereen't suppose to claim yourself in prior years.