Help! 5 1/2 month old waking 2-3 times a night.

Kelly
I have a great nighttime routine. Nurse my son, put his jams on, read a story or two, lay him to bed drowsy and he falls asleep. AWESOME!! 
NOT! 
Some nights he wakes after an hour, others he wakes after 3. He will NOT go back to sleep (we have don't every method) until I nurse him. I hate hearing him cry, but I let him cry once (Ferber method??) he wouldn't give up after two hours, ended in him throwing up. 
Same thing with naps. He won't nap longer than 20 minutes if he is not in his car seat or stroller walk. Me, my husband and my two school agers are EXHAUSTED and frustrated. Any help?! Advice?! 
He is such a happy, busy, thriving boy during the day. I am clueless!!!!