LO is just about 3 months old; I'm a FTM. I fear I made the mistake of letting him sleep on me these past few months. He would not get any sleep any other way... we tried pack and plays, numerous bassinets (flat and angled), swings, co-sleeper bassinets in our bed, everything. Swaddled and unswaddled. Eventually I let him sleep on me because it is the only way he would get any rest

I have two weeks until I go back to work and I'm getting worried about keeping this up. MIL will also be taking care of him during the day and I worry it's going to be very hard on her if she can't even get him to take a nap or two out of her arms. Any suggestions on getting him in a crib or similar?
Re: Getting LO to sleep in crib
I suggest watching "Happiest Baby on the Block" ... just swaddling alone didn't work for us either. The 5 S's from happiest baby made all the difference. Also, my DS wouldn't sleep flat for a while, have you tried a rock-n-play sleeper?
Do you put your LO down when awake on his/her back just to play when they are happy? It is very easy to sit and hold that first baby a lot.
We did with our DS 1.
Just remember, this phase won't last forever. GL to you!
So I tell you all that to say-- I think your LO will do it when he's ready. Mine did and I thought he never would unless I just let him cry it out which I wasn't about to do.