I weigh 85 to 100 pounds.
That's a huge weight range for yourself...most people don't fluctuate more than 5 pounds in a given day. Odd.
In any case, the lighter the ball the easier it will be in multiple gaming sessions...however, it's also "easier" to swing the wrong way if you have muscle and use a lighter ball.
I used to average north of 180 per game and used a ball that was around 11-13% of my body weight...it's hard to recall as this was over a decade ago, but I was in pretty decent shape at the time.
Stance and form are the biggest issues...try a lighter ball until you have consistant, accurate and on target throwing and technique...then if you feel the need, move to a heavier ball.
One thing on my weight I do not want to put any thing real personal out their,I am not dumb.
The general rule is about 10% of your body weight.
it should be around 15 to 20 %