Ladies!! Does this happen to you?

Sierra • Hi! My name is Sierra. & I`m a momma of a two year old girl (:
Occasionally, I get blisters on between my butt cheeks. They can be painful to sit on. I assume they are from panties, tight pants or too much moisture after intercourse without a condom.( as you could know that can be messy!!) 
I'm not sure but I'm wondering does anyone else have this happen to you? 
Or know what this could be from? And no it's not an STD OR STI I've had my Pap smear and been checked by the doctor. 

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