High Fever & Diarrhoea

Hi mummies my son has been sick since he started infant care. Which is 1st Aug, he is turning 15 months soon. High fever cough flu the first week(7days) then he recovered for 1 week(5days) and he is back to being sick high fever and diarrhoea for 9 days, I don’t know if it’s the school cos he likes to put things in his mouth or because he is teething. Cos at the same time I realise he is drooling so much and he has 3 tooth’s coming out. Keep going to A&E cos the fever(highest 40.5 lowest 38) and drooling is quite bad, he refuses to drink water and milk as I have force him with syringe. Doctors refused to take blood test keeps saying it’s a viral infection and he will recover himself He poops green with mucus about 8 times per day. His butt and penis is so red and stinging for him. So worried and I don’t know what else to do.