Before trying a much heavier ball, try to utilize different hand and finger positions in order to change your entry angle. You may find that by creating a different angles, rather than changing speed, will allow you to carry a bit better. Furthermore, you may want to try to walk on the approach slower, this will allow you to slow your arm swing down, creating a more fluid arm swing, instead of muscling the ball into the back swing.
A trick to check and see if it truly is the ball weight, is to place the ball in your bowling hand for five seconds. If the ball feels like nothing is there, then it is too light for you. You should feel a little bit of tension on your body with the proper weight. Best way is to go to a trusted pro shop and discuss the possibility of a ball weight change and see if they have time to watch you bowl. Good Luck.
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James