Infant rash help!

My LO is 6 weeks old and has had the clearest skin up until she turned exactly 6 weeks old.  I noticed a rash on the left side of her face Saturday morning (like the photo below) and thought that maybe it was a reaction to a lotion I was wearing since there are also bumps under and behind her ear and on her neck and they look like the bumps below.  Yesterday I noticed the rash has spread to the other side as well and is also under and behind her ears and on the side of her neck.  At first I thought maybe it was just a bad breakout of infant acne but now I'm thinking it's either seborrhic dermatitis since its on her temples and near her hairline or a gnarly heat rash even though it's just on her face and neck.  Any idea what this could be? I was going to call the dr but I've read where rashes on infants are super common and was wanting to know if it's something I can treat myself.