Sleeping on his belly 😫

My son in almost 3 months old and he did ok in his crib but now the only way he actually falls asleep is his belly on my belly. I wait about 15 minutes then lay him down but lately he only sleeps about 2 hours in his crib then cries. As soon as I pick him up and put him on my belly, he's out cold and it's a never ending (sleepless) cycle. I don't know if I did this to myself or if it's a phase? Has anyone else had this? If so how/when did it end?