16 yrs, i vomit every time i eat, and have painful kidney?

Hello, I am 16 years old. I am a female. I was on fluoxetine hydrochloride (prozac)off it now. For a year now, every time I eat I vomit shortly after (two t five minuts) this can . Every meal no matter what i eat. most fluids come back up too. even when i haven't ate for a while i ca still be sick. i have had barium swallow - normal, helicobacter test - normal, ultrasound - non cancerous cyst on liver, had blood tests done, times coming back low potassium never had my thyroid checked. really cold and lost a bit of weight not alot. every meal i eat i vomit - this is involuntary, i dont do anything to self inflict this. i am currently on the laxtive lactulose, for constipation, my left kidney sometimes gets so painful i think its too much water retention cause if i am sick and lots of fluid comes up it goes away, i get a sharp pain under my rib cage (left).