Help! Round bump!

So today I have been feeling like soreness right under my buttcheek. I thought I was just sore. I took off my jeans like 3 hours ago when I noticed that I have a painful red bump right under my buttcheek. I thought it was a bite, but it doesn't  itch at all! It just hurts and it's hard and round. It's as big as a dime. Idk what it is? I can't sit on hard surfaces either because it hurts so much! Ann's when I walk it hurts a lot too! The only difference I did today was sitting down for 4 hours for a training? Could that have caused it?