Post basal joint surgery-terible itch inside cast

I had surgery on my left thumb (dominant hand) a few weeks ago. A couple days after he re-wrapped my hand, I was having severe pain in my left shoulder and assuming it was related to the thumb surgery, I went back to the surgeon. He unwrapped again, sent me for shoulder xrays and told me my rotator cuff is thinning. He then removed the stitches and put a fiberglass cast on me 4 ays earlier than planned. He said the cast would be removed in 3 weeks-this is sooner thn expected, and I am happy that things seem to be healing well-except, my thumb (in the area of the wound) is so itchy and sore I'm practcally climbing the walls! Is this normal or should I risk looking like a wuss and ask the surgeon to take another look? I haven't had a cast on over a wound before so I'm not sure what to expect.