The only way you're really going to know is to see a dr. and have a colonoscopy done.
Don't jump the gun and think you have colon cancer, it could be other things too, like hemorhoids (as you've mentioned), or a fissure etc..
Your body is telling you something, so do yourself a favor and get it checked out. It may turn out to be nothing and you will have put your mind at ease. That'll be worth it.