What Causes Pain In Buttocks While Sitting?

My bum hurts when i sit in a certain position, also if i strain a little like i have to move my bowels it hurts, it doesn't hurt when i actually do go to the bathroom. i have hemmroids, could this be something to do with that? it is up further than my anus, sort of by my tailbone, i don't remember doing anything that could have hurt it.