When I first started throwing in earnest my finger with the string attached was really sore for a while. After a short time it got better. It sounds to me however your catch is your problem. It shouldn’t be. With your hand dexterity and coordination I’m certain you will be able to get this straightened out with some slight tweaking.
Here’s my suggestion; have you watched all of André’s beginner videos? I don’t wish to discredit your skill level, but a little review of the fundamentals may go a long way towards refining the quirks in your throw and catch which are giving you trouble.
Please remember this, you can always come here to this forum with questions. You’ll find a welcoming community anxious to help you advance. That’s what they’re all about here.
(well, there are a couple of jerks here, but just like Princess Bride’s flame spurts in the Fire Swamp they make a peculiar clicking sound just before they go off, so you soon learn how to avoid them.)
(make sure you have watched André’s tutorials under “Learn”. it’ll help you I think.)