6 week old baby doesnt like sleepin flat on his back...is it ok to put him 2 sleep on his bouncer?

when i try to put him 2 sleep on his crib he wakes up right away and starts crying. he sounds congested so i use some saline drops but he still sounds congested. when i put him on his bouncer or his swing he sleeps for hours. so is it ok for him 2 sleep on his bouncer at night?? and what can i do about his congestion??