Very severe pain in colon?

For the past several months I get this severe pain in my anus/colon. It usually only last a minute or two, but sometimes much longer- like 20 mins. Its almost impossible to sit down when I have the pain. I don't think its hemerroids or gas. The pain is very severe to the point where I almost want to go to the emergency room. Does anyone have any idea what this could be?