Is that a heat rash?

It's been hot here- most of the summer has just been really hot. Little man loves to be outside and he gets hot quickly. On Friday, he had some heat rash in the evening- it was purple spots all down his face (temple to chin along his cheeks) and then on his shoulder blades and collar bone. A diaper change revealed some in his groin as well. Fits typical heat rash, except I've never seen this weird purple color.  If it's not a heat rash, what is it? I assumed it would go away that night, but it was still there the next morning. It flares up and down....just odd rash, it is purple- like someone had a paintbrush and splattered it on him. And over the weekend, it isn't going away. He's becoming more "punky"- tired, cranky, warm, appetite up and down. By Sunday evening, I decide I need to check with his pediatrician in the morning. Monday morning comes and I decided to see how he did throughout the day first as he seemed better, was the rash lighter? He played well for a few hours, while I was making some formula....and then he started crying and the crying quickly escalated to screaming and of course that rash was flaring....he wanted to be held, he didn't want to be held, laying on the floor thrashing around, and did I say screaming?
I changed my mind, maybe there is more to this rash and it needs to be checked out. I called to see if I can still get an appointment, or at least a message to his pediatrician. The scheduler informs me that his pediatrician is not available....little man is screaming and I simply can't think, so I want to see another provider? Not really....a screaming child, 3 other active boys and trying to explain to a new pediatrician completely unfamiliar with little man (much less FPIES) that I am not sure if this is something FPIES related or just a rash....while giving me the reassurance I need that I was listened to and my son was cared for. We've been in those appointments before: deer-in-the-headlights look from doctors and me left standing there wondering why I bothered to leave the house but knowing my son needed to be evaluated.

I called Little man's daddy at work, as he was waiting for an update. I don't know what to do next, and I need to work on calming little man down. Put him in a bath, he suggests and he will call our pediatrician's office while I get try to get him calmed down. The bath does nothing but escalate him, which only reconfirms that something is just not right; but a bottle and a snuggle in the rocking chair finally calm him down and he falls asleep in pure exhaustion.
Little Man's daddy calls back, he has discussed the symptoms with the nurse and they urge that he either needs to be seen by another provider within the next few hours, or he needs to be taken to the ER. The rash description and symptoms are too concerning. Jeremy decides to come home for an hour with the other boys while I go bring little man in, in case he decides to do this screaming episode again.
I take him in and the doctor agrees the rash is concerning, coupled with his red-swollen gums, and symptoms, she wants to run some bloodwork to check on a few things (ITP, viral,....) then she wanted to make some calls to Infectious Disease on how to proceed.

We go home and wait to hear from Infectious Disease, and then go back to the lab for the bloodwork. The bloodwork is back....no doctor has made any return calls, but I can view them in an online account for patients and they are all fine. His CBC is off- showing his body is fighting something, likely viral (or reacting?!)...and his hemoglobin is falling again (as also happens when reacting).

So, what is this rash? Still do not know, but we are crossing things off the list and I get more concerned it may be from the probiotic. Now, the question is: is he reacting to the probiotic or is his body struggling with the upregulation of his immune system from