3 weeks late, 4 neg urine test, lower back pain,. cramps, classic symptoms? Or sick?

Hi, I'm nearly 3 weeks late on my period. I've taken 4 urine test, all of which are negative. A week ago I had severe lower back pain, and the sensation of dull cramps, this afternoon I threw up. It was bright yellow and diarrhea that looks similar. I've taken birth control(microgestin fe 1.5/30) in the past for 3 months but stopped for 2. I'm usually regular, my periods last 6-7 days, I've been really REALLY moody. I have ALOT of food aversion, I can't really eat very much, I feel sick or just feel full. I'm just feeling miserable. Oh and I get hot flashes from throughout the day at random.