Can't get him down at night

My 12 week old goes down for naps during the day in his crib so easily.  The last couple of nights we can't get him to go to bed. We do our bedtime routine and he'll be drowsy and/or sleeping when we put him down in his crib and immediately is up and fussy.  You pick him up, he's out again. He will go to sleep in the rock n play which we are trying to transition out of.  Is this normal?  I go back to work tomorrow and I'm exhausted!!