Red bumps


Does anyone know what this could possibly be?? They pop up and disappear within like 10-15 minutes. Some look like bug bites and some look kind of like hives. But they definitely aren’t bug bites cause I watch them just pop up in random places. Someone help this has been happening for 3 days now. He has a 6 month check up in 3 days I can move it up if I need to! TIA