Why can I not get pregnant again?

My husband and I are trying for a baby but I don't think I can. When I was 17 I got pregnant. It happened on my first time. I decided to keep the baby but ended up having a miscarriage three months in. I'm afraid this might be a reason. I am 21 now and can not get pregnant. I am getting very discouraged. So much as my sex drive has plummeted. I don't know what to do. I can not afford to go see a doctor as I have no insurance right now. We wont for a couple more months. Could there be a problem with me? Is there a chance the miscarriage did this to me? Any help would be great.