What Causes A Boil Below The Buttocks?

I have had a boil on the back of my thigh (right underneath my cheek) or a few months now. It went down and seemed like it was going away without draining, within the last week it swelled up again (not very huge). I've done so many hot compresses, epsom salt baths, tried Prid Drawing Salve. A bit of liquid came out but not all and it is still hard. Should I try using ichthammol ointment?