6 weeks old- Rash?

So my son is 6 weeks and 3 days — today he started getting this rash on the left side of his face and on his left leg.

He does primarily sleep on his left side.

I tried putting some breast milk on his face like I do when he gets little baby acne or a scratch and it hasn’t helped. But his skin is 95% of the time perfectly clear and smooth.

He ate less than 2 hours ago- he usually eats every 3.5 hours- and just now he had been asleep for 20 minutes post bottle/play time— and woke up hysterical with a cry he hasn’t had before and wouldn’t calm down until I let him nurse and he’s not even really eating he’s just using me as a pacifier but won’t take his paci like normal??

Any advice on the rash or how I can help him?