Like most medications the side effects should settled down within a couple if weeks, I know it doesn't make it any easier right now but you will start to feel better and by sounds of it you need to be on your meds so just try and ride it out it will get better
I'm taking the slow release lithium too , i switched from the normal lithium and i'm doing fine lately apart from the deep depression last week but that was due to a relationship break up , what you may be experienceing are side effects and should pass if not after a wek or 2 i would speak to our DR .
Side effects often go away within a few weeks. If the side effects are absolutely unbearable, talk to your doctor about trying something else.