Hello! Thank you for the query. Constipation and diarrhea alternately usually indicate partial bowels obstruction. Especially if nausea and abdominal pain appears. Gas is obstructed with constipation. Such obstruction can be caused by abdominal adhesions (if C-section has been performed), inflammatory bowels disease (like Crohns disease) or other intestinal diseases. Bad diet (lack of fiber rich products, low mineral water intake), severe bacterial infection, thyroid diseases, medicines (antidepressants, Ca-blockers) can be also a reason of such symptoms. Hemorrhoids and anal fissure seems to be only a result of constipation, therefore its treatment should be started with getting rid of constipation. I suggest you to visit gastroenterologist, have physical examination and consider colonoscopy and abdominal CT with oral contrast (enteroclysis). Stool tests should be also done. Hope this will help. Regards.