What Causes Lumpy Patch Of Skin Near The Buttocks?

I am a 18 year old white male, i have a patch of skin that has became lumpy and very iritated when i sit and walk, especially walking hurts i have had to change my whole walk to get around, this just started randomly 2 days ago when i woke up, the patch seems almost like 3 big zits where my butt cheek meets my left leg...any ideas?