What Causes Recurring Cystitis?

The flesh underneath my skin around my butt area (hope it makes sense and isn t creepy) is usually cold, even in summer when I am feeling very hot and sweaty. It is also cold when I try to warm it up. When this pairs with me walking around with socks of normal thickness for one second, it directly results in cystitis. My questions are: how does that cause cystitis, how do I prevent cystitis that comes up almost in every two weeks and why do I have a cold butt even when I keep myself warm?