F/18 bad pain lwr left ab cnstption (gp- miralax, (polyethylene glycol) now bm evry 5-7 days, pencil thin, square shape) bloat cant eat (vomit) chst pain ftgue ideas?

Go back to GP: go back to see your GP, this may be bad constipation or it may be something more serious. Someone need to feel your belly and you may need some imaging or a colonoscopy to prove nothing else is going on. In the meantime it is safe to take miralax (polyethylene glycol) twice a day to encourage BMs no matter what the underlying cause.