What could be wrong with my two year old?

i noticed that this morning he didnt want to eat and he barely ate his lunh and we even offered a cookie and he didnt want it..at about 2 this afternoon he cried and cried for an hour in a half before ping out he just wanted to be held and wouldnt accept anything he has woken up 3 times cried and cried then went back to sleep he has a slight fever of 100.00 but i did give him some motrin.i think it might be his throat or ear but hes never cried like this before??any tips??what should i do? doctor or let it run its course? what do you think it could be