Advice needed about rash, please!

So, to cut a really long story short, 2 months ago my now 8 month old son had a leukemia scare, after lots and lots of blood tests it was decided that it wasn't leukemia and was infact a viral infection but 2 months later and there was still abnormal cells showing but whatever doctors know best?.. so yesterday lo came out in a rash, no temperature not unwell in any way all normal but this rash all over his belly, tiny red pin prick dots. I thought it was perhaps heat rash (although he wasn't overly warm) today it's still there but no were near as bad, my concern is that it could be petachiea (symptom of leukemia or a number of other things) could anyone take a look for me and see what they think, will show you yesterday's picture and today's thanks in advance!