Mostly happens at night? Sounds like scabies to me. If it is, you can get some lotion from your Doc that will kill it instantly. Did it start out small and then spread gradually?
From mayoclinic.com:
Almost impossible to see without a magnifying glass, scabies mites cause itching by burrowing under the skin. Itching is usually worse at night. The burrowing leaves tiny bumps and thin, irregular, pencil-like marks or tracks on your skin. They appear most often in the following areas: between your fingers, in your armpits, around your waist, along the insides of your wrists, on the back of your elbows, on your ankles and soles of your feet, around your breasts and genitals and on your buttocks. However, almost any part of the skin may be involved.
Close physical contact and, less often, sharing clothing or bedding with an infected person can spread these tiny mites. Often an entire family or members of a day-care group or school class will experience scabies.