So my girlfriend has never gotten a period due to the fact she has been on antipsychotics and seizure meds all her life. we want to get pregnant but is that possible if she's never had a period?

I would not assume she has not had a period because of mental health meds. Some women are born without all the parts, including a lack of a uterus or connection between the parts that allow menses. If she has all the parts, some seizure meds create devastating birth defects. Before trying for pregnancy, a consultation with a clinical geneticist to evaluate the risks would be prudent.