Thank you for your query, Would you please clarify a few things for me? 1)how old is your son? 2)would you describe the rash? (colour, does it blanch on pressure? Is it itchy? Does it have a different colour on the base or any fluid in it? 3) has his sore throat been cured? How long has he had the rash for? 4)you mentioned him being tired- is he too sleepy or difficult to wake? Does he refuse food or being held by you? Does he have vomiting? Any jerry movements or staring expression? Rashes occur in many viral and bacterial illnesses and usually goes away on its own. If, however, it gets worse causing discomfort or associated other significant symptoms (severe skin peeling, infection of the rash, high fever, marked lethargy, pale or blotched skin, poor food intake, rash that doesn t blanch on pressure) occur, a trip to the ER is warranted. Blanching is whitening of the rash of pressure (use a glass cup so that you see through while applying pressure) Rashes (reddish brown) that start behind the ear occurs in Measles. Sore throat, fever, lethargy also occur. Rashes (pink-red) on the face that spreads to body and lasts for around 3days occurs in Rubella (unlikely if vaccinated) Some fatigue is expected after an illness but if your answer to any of the questions in number 4 is yes , that needs to be checked out right away. (possibility of meningitis infection of the membranes that surround the brain) I recommend seeing his pediatrician who could have a look and reassure you and do the needful. Answers to the above questions will help to arrive at a diagnosis. In the meantime, keep him hydrated, give small and frequent nutritious meals and snacks. Keep a close eye on him and monitor the rash and his overall behavior. Write it down, this will help to compare the observations. Hope this helps. Please let us know if you have any other questions? Wish you both good health.