I inserted my finger into my anus and on the wall closest to my vagina i can feel a firm structure / mass what is this?

There is no way to diagnose this without examining you. So, you need to see your doctor and have it evaluated. You may need to be seen by a GI doctor. Good luck to you!

When we perform a bimanual rectal examination on a woman, we can palpate the cervix which feels firm. For you to do this on yourself while lying on your back would be remarkable but possible. I suspect that that firm mass you felt anterior to your rectum was your cervix which may be part of a retroverted uterus. Your MD or gynecologist could confirm this.