Hello, Welcome to Health Care Magic. Thanks for writing. I am Dr.Saddiq ul Abidin. I have read you question completely, i understand your concern and will try to help you in best way possible. I am sorry to know what is happening to your son. It is usually normal in viral infections to get a rash , like hives or something but in your son s case it s timing is a bit dicey , he was having infection for seven days and hives came out today. This suggests to me that he might be having allergy due to the virus that caused diarrhoea but he could be having a separate allergy , you will have to consider possible causes, did he take any new medicine ? that is a very important cause to consider. As far as the treatment is concerned you don t have to give him any new medicine except an OTC antihistamine syrup which will hopefully help with his problem. But if after the syrup is given still the problem stays there or gets worsened do contact your doctor he might want to rule out a few things like viral skin infection or severe allergic reaction. I would suggest you not to panic things will get better soon because according to history you gave, you son is already improving. Hopefully in 4-5 days he will be all fine. Just take care of his nutrition and hydration status. I hope this answered your question.If you have more queries I am happy to answer.Otherwise rate and close the discussion Regrads. Dr.Saddiq ul Abidin M.B.B.S(Licensed Family Physician) Resident Medicine.