HI Well come to HCM Thank for asking to HCM, I had gone through the history given here and I could say that it pretty common condition seen in pediatric patient and it is not due to any disease but it could be due to some nonspecific reason, it may not need any treatment but it is the self limiting condition will come around on its own, just care needs to be taken for dehydration, for the rash, antibiotic can be tried if ever it is the bacterial infection of the GI tract, but better to wait for some time prior to start the anti-biotic or have a word with pediatrician hope this information helps.