Baby is not sleeping (long sorry)

Please help, I am at my wits end. My son is 7 1/2 months old. Since he was 4 months old he has slept through the night, waking up about 7 AM. For the last week, all that has changed. He falls asleep at 9 and is up at 3 screaming. Previously, if he woke up I never picked him up I just rubbed his bottom and he'd fall right back to sleep. Now I have to rock him, he passes out in my arms within 2 minutes and is up the minute he gets back down on the mattress. Or he'll fall asleep 30-40 minutes and starts screaming again.
However if I lay him on my bed, he rolls over, puts his thumb in his mouth and is off to dreamland. My husband says I should just let him sleep there but I can't get into that habit. A few times I gave up and caved to save my own sanity.
He just got 2 teeth. I don't think it's more teeth coming in yet because I've given him baby orajel, tylenol, and it doesnt help
Please help. I'd appreciate any help.

I don't know but maybe the baby just wants to be near you. Was the baby recently in your room and then you just moved him into his own room? Maybe the transition is going to take some time for him to get used to.
I hope he is able to sleep better soon.