No sex?

So me and my girlfriend have been dating for over a year and in the beginning we had sex two sometimes three time a week, obviously it kind of went down to once a week and it’s been once a month for like ten months and now she won’t have sex with me any more because she’s never in the mood, I’m a very sexual person and masturbation just doesn’t always cut it. I don’t feel wanted when she doesn’t want to be that intimate with me. And it’s not like she doesn’t get in the mood because she used to be in the mood all the time. Once a month isn’t enough for me, I understand not want to do it every week but like once over two weeks? She is on antidepressants and of course it does affect her but again she used to be in the mood all the time for the first 3-6 months of dating. What should I do? I have talked to her about how I feel unwanted but she can’t really do anything about it because I’m not about to force her or anything. Sometimes she was in the mood and I’m not completely in the mood but I’ll still do stuff for her. I don’t know what to do. If I can even do anything.