Experiencing lower back pain and pressure in pelvis. having diarrhea and constipation interchangeably. extreme amount of mucus in stool every time i use the bathroom. is this a parasitic infection?

There are many possible causes of such symptoms. In the US, parasitic infection is probably least common -- probably under one chance in a thousand (maybe a bit more likely if you have traveled to the tropics or a developing country). Your symptoms are most consistent with irritable bowel syndrome. Keep working with your doctor, or see a gastroenterologist. Good luck.