Excrutiating pain in my rectum?

3 month ago when i had a bowel movement there was blood on the tissue sometimes a lot as time went by the bowel movements started to hurt, the doctor thought i had fungus in my rectum that was 5-15-11 then the following week after i had the bowel movements these excrutiating pain would burn me from my rectum he gave me all these creams fiber pills stool softner and sitz bath and even if i dont have a bowel movement these burning pains would come and can last hours, he said i have an fissure i am not sure if he is rite, i cant understand from the amount of food i am eating a day which is so so minimal like water melon 6 egg whites water and gatorade i feel constipated