Pleas Help

Unexplained Rash on my 3 month old that won’t go away, developed around 2 months old. Extremely itchy and is causing hyperpigmentation. Doctors said it was a heat rash at first, then milk rash, and suggested I change the formula to nutramigen. I’ve kept his neck area clean, changed to that formula, and nothing is helping. Any suggestions?!

It has spread to his entire body, he has a lot of dandruff for his age.. I’m a ftm and I just hate it so much 😭