Well, im nowhere near a beginner but this seems like the best spot for this type of post.

I have been throwing the same ball for several months and just recently started tearing up the top of my thumb. I have never had tears or blisters on the top of my thumb before. What could this be from?

The blister is on the thumb on my right hand and is right on the left (outside) side of my knuckle.

What can I do to prevent this from happening? What am I doing wrong for this to start happening?

Any ideas?

There are many factors that cause blisters; improper pitch, weight gain, high fluid intake, natural/gradual changes in the human body, and sometimes even evolution of your own game. I would probably rule out the improper pitch because you said you've been using that ball for a while, but it's not out of the question, especially if your game has evolved. I would be more inclined to think of weight gain or fluid retention as the causes. Of course, if this is the first time you've rolled the ball since last season, then you have lost the callous from last year.

Regardless, you should go to your favorite Pro Shop and have your thumb checked in your ball. Most people don't realize how much their bodies change, even as an adult.

I've been throwing this same ball for several months and I bowl 15 to 30 games a weeks when im not in season.

It was fine up until last week. Maybe my thumb was swelled but I really felt like I was holding the ball fine (my thumb felt fine in the hole)

I guess I'll take a few days off to let it heal and see what happens.

Well, it's possible you could have been doing something different. Pulling a blister on either side of the thumb would indicate to me that your hand is in the ball in a way that's different as to what your pitches dictate. Not knowing your game, and having more information now, I would be willing to believe that you were rolling the ball or releasing it differently or might've been squeezing the ball. Either way, yeah, let it heal, and when you're ready to bowl again, get some skin patch and put it on there for a couple of weeks.