Anal inflating

My BF (m32) and I (F34) have recently started exploring my anal realm. He's the first guy I've ever allowed in back there but he's had experience with past GFs. After a couple times doing it now, I can honestly say it's much easier and wayyy more enjoyable than I ever thought it would be.

But my question is this - Does everyone fill up with all that air??? It can be very uncomfortable after only a couple minutes and it makes me feel super bloated and gross. He says to just let it out but I'm super self conscious and worried of what might happen. He has an average size member and we've tried multiple different positions. All with the same results. Just curious if all that air is normal??