First, I'd let your doctor know about the itching. Sometimes Benedryl (diphenhydramine) can help with allergic itching, as this does sound like it may be an allergic reaction. Again, check with your doctor first. Benedryl can make you feel sleepy, so be cautious with it.

As for your dosage, 150 mg really isn't that high. I think 200 mg is a common target dose, and I have been on up to 350mg before. That's about as high as they recommend for bipolar disorder, though they sometimes go higher in epileptics.