Really itchy skin, any suggestions?

I have had really itchy skin for about 6 weeks now. It started with my thighs, I went to see a doctor and they prescribed an ointment which I used for 2 weeks. It seems to help a little on the area where I used it, but as soon as I stopped using it came back full force and is now spreading. I have random small red rashes on my back, legs, and arms that itch so bad it wakes me up at night. I tried oatmeal bath and Eucerin anti-itch creme, but it only reduces the itching - it doesn't make it go away, and only works for a few hours. I haven't slept well for a few weeks now, and I am not sure what else I can do to get rid of this. We changed our laundry detergent a few months ago, but the itching didn't start until a few weeks ago, and it is the sensitive skin detergent - no dyes, or other chemicals. I have not changed any other products that I use. Thank you for any advice!!!