Is this a heat rash? Eczema?

I have been putting hydrocortisone on small spots just to test it out on my baby's skin. It seems to work but then in a couple of days later it's back. Is this a heat rash? I asked the doctor he said no but wasn't this bad when I showed him. She has tiny bumps on her neck and her back is all red too. I use Aveeno bath wash and lotion on her. I wash her clothes with All clear detergent and I tried putting aquaphor on her cuz I saw some dryness along with the redness but it doesn't help.  Any suggestions?