Swimming = bloated stomach … why?

Swim twice a week, a steady 50-60 lengths/25-30 mins, mostly front crawl. Have been doing this for a number of years as physio/maintainence of some back/shoulder injuries. Recently been getting a pretty uncomfortable bloated stomach immediately after swimming. No difference on time of day/when/what eaten. Haven’t changed swim style/stroke.

Guess my breathing’s not right (swallowing air somehow?) but am not pushing it when swimming (pretty gentle stuff), used to swim competitivenly so think my style is OK-ish.

Any ideas

PK Ripper had this- distended stomach I think is the right description?

Taking on chlorinated water?

it’s only just started happening in the last few months. and I don’t get a distended stomach any other time. Is quite uncomftable tho when it happens and is putting me off the swimming!