Tonya your doctor needs to be in the loop on your meds.
How long have you been on lithium? Some of the side effects become less after a month or two.
Dividing a capsule would be very inexact. And part of what makes lithium so effective is a steady amount in the bloodstream.
Before doing anything with your pills, I'd suggest calling your doctor's nurse and see about having a lithium level done to make sure that you're not at a toxic level.
They could then switch you to a tablet (although I'm not sure that every pharmacy or mail order place keeps both types on hand).