My Butt Hurts After Cardio, Why?

I know it sounds strange, but after I'm on the treadmill for 20 minutes (usually it reads that I've walked about 1.2 miles) at a brisk pace with a slight incline, my butt hurts. I change the pace gradually up during the session and I notice my butt cheeks hurt the rest of the day, especially when I sit down. Am I doing something wrong or should it do that?

I know, hahahaha, hilarious, I'm literally butthurt, but any serious opinions would be great.
My Butt Hurts After Cardio, Why?
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