Yesterday, after several minutes after pooping i took a shower and felt like an organ was out of my anus - doesnt feel like it anymore. today, i think i had mucus from anus. should i be concerned? is is cause im super underweight?

If you strained having the BM you may have had a temporary prolapse of the rectum. These are more common in older women who have had multiple pregnancies but can occur in younger women too. Avoid straining for BM's by drinking plenty of fluids and eating enough fiber. See your physician, gynecologist or a proctologist for evaluation if you still have concerns.

As a board certified internist and cardiologist you ask a great question. Did you strain or constipated? While this could be a prolapse or effect from constipation, the mucous and being 'super' underweight is a red flag for a malabsorptive or infective disorder. You should not have mucous in your stool. Consider a stool test or see a MD if this persists.