Sore knuckle from new ball (backup thrower)

I'm an amateur bowler, so I apologize for my lack of knowledge & lingo that I'm still learning. Until about 6 weeks ago, I threw an 11lb straight ball. My husband gifted me my first curving ball for Christmas, a 12lb Raw Hammer Pearl. I got it drilled with fingertip inserts at the shop, and upon throwing it for the first time, realized I throw a back-up ball. I'm right-handed and it curves to the right. It feels really natural to me to throw this way, it doesn't bother my wrist at all. I used a similar form with my straight ball. I've increased my average by about 30 points and see improvements each week (league). I practice throwing normally (curve to the left), mainly for spares, but it's unnatural and doesn't always go so well.

So my issue I'm hoping someone may have some insight to, is the top knuckle of my middle finger is sore and tender from bowling with the new ball. Since we bowl weekly, it doesn't fully recoup by the time the next league day rolls around, and it starts all over again.

I'm trying to figure out the exact cause of this. I thought it would adjust to the new use & weight on that finger, but so far it has not. I already replaced that insert with a looser one, as it was giving a bit of friction on the sides of my finger, but the pain persists. I think it's just the bulk of the weight is on that fingertip when I release and it's causing an overuse issue. Probably bad form? I'm learning that since I throw a backup ball, a ball drilled for a lefty would be better? Which sucks, since I just got the ball and it's drilled for a righty.

I'd appreciate any ideas that I can explore. Thank you!