Milk allergy or heat rash?

So my baby had this rash on her face Sunday. It was bad and now looks way better, a few bumps are still there but it looks very mild compared to this past weekend. I now notice a few in her hairline / forehead but very mild. She was sleeping on someone’s chest each night up until recently - so I was assuming it’s a heat rash/irritant to our detergent for our clothes? I also notice all of her dirty diapers the color is very dark green and it’s always runny. I usually get 1/day. Not sure if this is a milk allergy or heat rash. She is currently on similac pro total comfort. Debating switching to Nutramigen.

I would assume if it was a milk allergy rash it wouldn’t be starting to look better with continuing formula - she’s been on it for 1-2 weeks before the rash happened and I continued doing the formula and it looks improved.

We have been in contact with dr waiting to hear back - just wanted some other mamas input that have gone through milk allergy.

This picture is what it looked like Sunday.

Rash was only on face . Everywhere else on body looks normal.