infertility....

OK guys. Well where do I begin; I am 19 yo and just recently got out of a very long relationship. Since I was about 16 and started having sex I have had BABY FEVER! It's crazy. So me and my SO started trying. Nothing happened. I thought it was just because I was so young. We kept trying and trying. Still nothing. My period would be late sometimes and I'd be super excited and would test after the 2 week period like everyday. Still no baby. Then my period would come and be heavier than ever. Back in June we had unprotected sex like always and this time I propped my legs up for about an hour. Then got up. I am now almost 5 months late on my period. I tested in the middle of August via blood and I wasn't pregnant. Then the end of September I had another blood test because something didn't seem right. Still not pregnant. I keep thinking king I have symptoms (nausea  badly,slight cramps,tired all the time, food craving/aversion, etc) but I just can't get a positive test. What do I need to do.i feel like I'm getting chunky-ish but I could be gaining weight. Help!