Brief Answer:
Detailed investigations are required.

Detailed Answer:
Hi and thank you so much for this query.

The common causes of rectal bleeding include anal fissure, hemorrhoids, diverticulosis, colon cancer and polyps, colonic polyp removal, angiodysplasias, colitis, proctitis, and Meckel's diverticula.

When irritated, external hemorrhoids can itch or bleed. Thrombosed hemorrhoids. Sometimes blood may pool in an external hemorrhoid and form a clot Treatment greatly depends on the cause.

Initially i would suggest you to go for repeat colonoscopy and digital rectal examination in physical by a Gastroenterologist to rule out the above mentioned possibilities.As there is bleeding i would suggest you to meet your Gastroenterologist Asap.
Alternate constipation and diarrhea can be because of irritable bowel syndrome. It is a disorder of the large intestine.This constipation may be responsible for rectal bleed.

However i would recommend you some Lifestyle and Dietary changes by making several basic modifications to your regular diet and activities, IBS improves with time. Here are some tips:

Avoid caffeine in any form such as coffee, tea or soda.
Increase the amount of fiber in your diet and include vegetables, fruits, whole grains and nuts.
Drink three to four glasses of water regularly.
Smoking should be abstained from.
You must undertake relaxation techniques and work out in order to reduce stress.
Dairy product consumption must be reduced.
Try to eat frequent, small meals instead of fewer large meals.

Keep a record of the types of food you consume so that you can identify the IBS triggering food items.

Try to eliminate high gas producing food items from your diet. Food items which may result in passing excess amount of gas such as carbonated vegetables and vegetables such as cabbage, broccoli and cauliflower should not be consumed.

Take Metamucil 2tsf once daily before going to sleep.
Take a good quality probiotic like Econorm three times a day for atleast a month.

Both bleeding and irritable bowel may be connected to each other therefore a detailed review is important before coming to a final conclusion.

Thanks.

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