I feel your pain - my foot was purple with blisters on the sole of my foot at one point. The itching would wake me up at night.
There is a couple of things that you can do:
1. When you are itchy do not scratching. Icing your feet will stop the itching. I bought the flexible freezer packs so I could wrap my feet at night to be able to sleep.
2. Go see your dermatologist or your doctor to recommend a dermatologist. They are really the experts and will try a course of treatments to find the one that works for you.
The answer for me was a perscription of 60mg Dovobet ointment. It is a steriod but it works! I can were sandals again.