Hmmm, one problem could be that you are very sensitive to humidity with your hand and skin? You didn't wash your hand s in the meantime, did you? This COULD be a solution for this problem.
When your thumb is swollen after some games, them either the thumb hole should be checked (maybe by a third party?), or you could be gripping too tight to the ball upon release. I have similar problems which I fight currently with a longer approach and a deeper knee bend - but the symptoms end up in a blistered thumb (I am a righty, my thumb skin gets worn out just at the right thumb nail side).
If you can maintain a proper grip, then try to insert your thumb not too deep. But this is an individual solution - for me, for example, it does not work since I have rather slender fingers and thumb and need all of them inside if the ball to have a proper hold in the backswing.
Finally, I am going with AZ Guy: have somebody with a rep for being a sound ball driller watch you play, and have your ball checked. Proper ball fit is a prerequisite for success and enjoyable bowling, do not hamper yourself with ill-fitting equipment.
Gut Holz!
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DizzyFugu --- Reporting from Germany
"All that we see or seem, is but a dream within a dream..." - Edgar Allen Poe