antonetty, since you live in the USA and are 50ish, you must have had to have a birth certificate to get into schools and other things.
Who is listed as your mother on your birth certificate?
I had the same problem, I found out that my mother was not my birth mother at 18. What I did was request my birth certificate from the county I was born in and it had my real mothers name on the birth certificate.
Hope this helps
You should contact the vital statistics office in the state you were born. You can got to cdc.gov to get the phone number and address of your state's office. Or check the government pages of the phone book