plz help, baby isn't sleeping!

Mommies I need some serious serious help please!:( My baby is 3 months old and he is waking up screaming every time i try to lay him in his crib for bed!? He usually settles down well to bed around 12:30am-2:00am. And he has fell SOUND asleep about 5 times now in my arms since then (its now 5am) However every time I go to lay him back down he suddenly wakes and screams and will not not not sleep even if I let him cry it out a little. I can't figure out what's wrong?:( He's NEVER like this. Please help any suggestions! He's not showing signs of being sick, however he is starting to teeth I think?