Re: 3 month old constantly crying when not held!!
You've probably had lots of experience with crying babies, so you know the difference between when he's in pain or not, no doubt. But you always have to look at that first. Stomach pain, whatever.
But if you think its just for attention, or because he's used to being held, then most doctors say its OK to leave them cry for awhile. If it was me, I might strap him to my back with a baby carrier while I was doing my chores. Then, if he's not in pain, and the house is fairly quiet (!)lay him down, try to turn on some soothing music and do a foot massage with firm but gentle movements; start a routine. He might be overstimulated just a bit with so much going on all the time. Get him used to laying by himself with you laying next to him as opposed to you holding him. I made the mistake of breastfeeding my son to sleep, pretty soon, he was almost 2 and couldn't go to sleep without breastfeeding! Then every time I moved to get up, he would wake up, I never got anything done. Self-soothing is important for coping strategies for when they're older, but in my opinion, not with a bottle or a breast, unless they're in pain. It's healthier for them not to learn to depend on food to soothe their anxieties.
Best wishes, K.