Bleeding due to hard stool. Junk food?

From time to time i have been suffering with bleeding from rectum. earlier it used to be very mild and got cured on its own. but from the last one year it was taking 2-3 days to cure on its own. but since last 3-4 months back i had to show to a doctor who prescribed drinking milk of magnesia and applying hadensa gel in rectum before and after defecation.for couple of days i forgot to take the prescribed medicines and also ate junk food and again i faced same bleeding. again resumed with same medication. I consulted the same doctor again and he advised that I have to take milk of magnesia throughout my life. is it safe tk consume this liquid all my life? if not then what are the other options? why does this bleeding from rectum begins the moment i start having my favorite cheese and junk food?can i never eat junk food?