I don't know whether he is ok or not

My son hasn't been feeling right since Thursday last week, he's gone off his food completely but will happily eat chocolate or crisps, today I went to Costa with my friend and bought him a Cookie....he didn't eat it and he was so tired but only slept for 20 mins his temp is on 37.7 tonight, last night he did nothing but cry and I tried everything to get him to calm down, in the end I had to leave him fight himself to sleep, he normally sleeps really good at night too, he's grumpy, always wanting to know were i am, calls me if daddy is having to deal with him at the time like after a bath because I sort my daughter out, he's drinking quite alot of water were he's filling himself up, his breathing is more rapid I have noticed, tonight I tried to give him food and he gagged on it and spat it out, he then purped as if he was going to throw up, he does look pale and under his eyes are red, I also noticed a couple of spots appeared but they are just about going now so I'm not sure, I thought it may be his teeth but I can't see any coming through, maybe upset tummy i don't know, but I hope he doesn't stay awake all night again tonight, my head can't take another 4 hour sleep, he's also 2 years old just incase that helps