You have not told us how long ago you began living with your GF----most likely your mother can still claim you as a qualifying child dependent on her tax return. If there are details that mean you have not lived with your parent for even half of 2021, then we would need to know about that.
You can still file your own tax return but you need to say that you can be claimed as someone else's dependent. Your income cannot be entered on a parent's income tax return. But parents receive child-related credits for claiming you as a dependent, and they will want to get those credits.
You say that you had self-employment income. That means you have to pay self employment tax if you made at least $400 in 2021. You pay that for Social Security and Medicare.
https://ttlc.intuit.com/questions/2926899-how-does-my-side-job-affect-my-taxes
https://ttlc.intuit.com/community/self-employed/help/how-do-i-report-income-from-self-employment/00/...
https://ttlc.intuit.com/community/self-employed/help/what-is-the-self-employment-tax/00/25922
https://ttlc.intuit.com/questions/2902389-why-am-i-paying-self-employment-tax
https://ttlc.intuit.com/questions/1901340-where-do-i-enter-schedule-c
https://ttlc.intuit.com/questions/3398950-what-self-employed-expenses-can-i-deduct
https://ttlc.intuit.com/questions/1901110-do-i-need-to-make-estimated-tax-payments-to-the-irs
To avoid paying the expensive fee to use online Self-Employed software, you should wait until later in January and try the free software that will be available on the IRS site:
https://apps.irs.gov/app/freeFile/
**Disclaimer: Every effort has been made to offer the most correct information possible. The poster disclaims any legal responsibility for the accuracy of the information that is contained in this post.**
