Why Don't I Have a Sex Drive?

I'm 22 years old with no sex drive. Sex isn't always fun for me anyways, but I thought I was supposed to be like "constantly horny" at this age. I have HPV and have battled endometriosis as well in the past year. I have a fiance I have dated for the past two years. He's pretty supportive but sometimes takes offense to my lack of sex drive. I'm on the pill and anti-depressants as well. Does anyone know why this is? I've heard that all three things (the pill, anti depressants, and endometriosis) can contribute to this...but how can I help it? We will be married in September and I don't want to be like this my whole life. I hate it for us both. Please help!