Digerstive system problems!! help?

Hi im 14, female in mid-july i got constipated for no reason I never got constipated it was sudden. I tried laxatives prune juice more fibre everything, Im really fit too. Nothing worked exept docolax, I went to the doctor and he just said more water, fibre fruits he gave me laculose. Laculose worked once and never again im back to square 1, then I got this shrap stabbing pain on my left side near my hip it was horrible! he sent me for a ultrasound they found nothing, then my pain shifted to my right side and it hurts but not as much as my left, since the middle of july till now nov 12 ive been severly constipated and I really want the doctor to find out what i have! does anyone think they know what i have? I think im gunna need to take a higher dosage of docolax but it kills me i almost p out and i have a fever but i feel extreamly cold i get extreamly nauseous the next day and my stomach hurts so bad !! CAN ANYONE HELP ME PLEASE.. do i have cancer? cause i read online that i might.. can anyone help./!