2 months late but no positive pregnancy test?

I'm 16 and I haven't had my period for two months and I think i'm pregnant, but all my tests say negative. I don't really know what's going on with my body! Everyone says i'm crazy..... My symptoms include nausea, discharge, fatigue, eating more, weight gain, tender breasts, lower back pain, cravings, and missed period obviously. My stomach is sitting too low for fat and it's definitely not squishy. In about a week and a half I went from wearing a size 3 with a belt to a 7 comfortably fitting. My pants don't fit! My doctor says it's a virus, but viruses just don't do this. My mom said it's just my body changing from having sex.....but none of my friends went through this. Please help, even my parents don't believe me.