I dont know why, but if it was me and i couldnt fix the problem "going down the list." Not hungry, not cranky, holding em isnt helping... ect.. Take him to the doctor, it doesnt hurt just to know. They will be able to help.
My daughter is doing the same thing!! I'm taking her to the doc tomorrow to make sure there is no ear infections. I don't know what else it could be. She got two teeth a week ago so my last thought is that it's teething.