What is causing me to bleed from ?

I was bleeding from my when I would have bowel movement. I went to Dr and had colonoscopy and egd done. Nothing found on egd. A little hemmorhoid was found on inside. I had a baby 4 months ago also but didnt have any problems then or after giving birth. bleeding didnt start until after month or 2 after giving birth but dont know if that could have anything to do with or not. It was very hard delivery...big baby, she got stuck...all natural, no epidural.I had CAT scan, too and nothing found.but i couldnt keep contrast down so dont know if something just didnt show up because of that. but bleeding stopped for about two wks and now is back. well i started thinking and realized its worse every time after i eat fish at long john silver. well i havent ate there in like 2 wks and did today and the bleeding is back. my stomach will hurt horribly bad before I go to bathroom and bleed. and it is coming out of my , not my ...its not period or anything like that. its bright red blood sometimes and sometimes dark red blood. its not light blood. its ALOT but my hemoglobin has been fine when checked. but drs have seen how much blood and said that its wayy too much to be ping and dont understand how hemoglobin is so good after that. please give me some suggestions on what it may be if fish can cause anything like this...also everytime i eat fish my daughter breaks out after eating (shes fed).