What causes itching but no rash? My upper arms and shoulders itch at night.?

I'm trying to determine what causes this severe itching.I don't have a rash, but the scratching is irritating my skin. Last night I drank a red wine (cabernet Sauvignon) with dinner and started itching. THis has been going on for some time now, and I am trying to deternime the cuase. I started taking symvastatin for cholesterol several months ago and thought that might be causing the itching, as I take it at night. I quit taking it for several days and thought that might be the problem. But then when I drank the red wine last night and started itching again, I'm wondering if that could be the problem. The itching occurs primarily at night and if I drink red wine, it is usually in the evening also. Any insight?