Tips on dealing with a high maintenance baby

My three month old baby is high maintenance. He cries a ton, even when he's been fed, changed, and entertained, and it frustrates me that i can't figure out how to soothe him. He also isn't a great napper, even though we've been working on it, and I feel exhausted because I never get a break. He only wants to be held by me and screams within thirty seconds of anyone else holding him. He has his happy moments but can turn on a dime. This all seems to have gotten worse as he's getting older, and I'm at my wit's end.

So parents of difficult babies, any tips? Did your baby settle down, and if so, when? Thanks for your advice!