Help! Needing sleep advice

My son is 12 weeks old, and sleeps in a bassinet of a pack and play next to our bed.  For the past 3 nights, he will not fall asleep in his bed until 12 or 1:30 am - and we start our bedtime routine hours earlier!  He wants to be rocked to sleep but when I place him in the bassinet he wakes up within 15-20 min and cries.  I pick him up and We then continue the cycle.  I don't want to let him CIO .. Any tips?  I'm so tired!  😕