A rash started behind my knees 3 months ago. My whole body is now covered. I have a higher cortisol level. I am pregnant. What will take the itch away?

This sounds pretty. difficult especially since you are pregnant. You need to see your health care practitioner and get checked out. You might need a referral to a dermatologist. Oatmeal baths may be the only way to go until after you deliver.