The pill and butt pimples?

Dylan
Shortly after I started taking the pill I've started getting what appears to be pimples on my butt. They don't itch or hurt (unless I mess with them then they're a little tender) 
I notice they're larger in the evening and almost gone by morning so I think friction from walking around all day is aggravating them. 
Has anyone had this happen? Is it a side affect from the pill? Or just an odd coincidence they started up around the same time. 
Side note. I have acne on my face and occasionally get it on my back and chest. I'm fairly positive that's what it is on my behind. I also have really sensitive skin though too so maybe it's just a reaction to dry skin/friction from my underwear or pants/or a reaction to a new laundry soap or body wash or something