I am almost 37 weeks pregnant and I have a rash on my belly and is extremely itchy. What could it be? 37 weeks pregnant g4p2, otherwise healthy

Many potentials. Some people develop an ugly looking rash during pregnancy which is often treated with a short-course of cortisone. On the other hand, you can also have a contact allergy. See your doctor about it.
It . It is very importnant that you have this rash assessed by your doctor as soon as possible. The rash could be benign and a result of creams you may have used. It can also be pupp - pruritic urticarial papules and plaques of pregnancy (puppp) or polymorphic eruption of pregnancy. This typically presents in the 3 trimester of pregnancy and may look like blisters or hives on the skin. Your doctor will want to see you to assess the rash and recommend a treatment regimen. Worst case scenario is that intrahepatic cholestasis of pregnancy, a rare liver problem where bile salts that normally flow to the bile duct accumulate in the skin causing skin to be irritated and itchy. This condition requires emergent medical condition because it can cause your baby to be distressed. See your doctor asap.