My husband and I have always said it’s too bad children don’t come with their own personalized user’s manual. Each one is different so what works for one, even in the same family, may not work for the other. So don’t be discouraged as you try to figure out how to help your sweet boy.
Having mostly eliminated the teething, ear infection and hunger as causes, what you describe could be separation anxiety. This can be significant for some babies. It sounds like physical contact with you makes him feel more comfortable so this is my best guess. Some research on separation anxiety may help you decide how to proceed. I think this article is a good one
http://bit.ly/28NHaIV
I’m sure you, your husband and your 4yo are losing sleep too, which makes everyone cranky but hang in there, you’ll get thru this.