I have a 5 month old and while each baby is different, it sound like you're forcing too many naps on him.
My daughter follows this schedule:
6:30-6:45 Wake Up
9:00-11:00 Nap 1
11:00-1:30 playtime
1:30-3:00/3:30 Nap 2
then after nap 2, she generally chooses wether to take her third nap of the day, which we never let her sleep more then 30 minutes...so she averages 6pm-6:30 for the last nap of the day (if she takes it, if she's awake at 6:15 we cancel nap 3), then she gets up and does bedtime routine (bath, play in sister's room until grumpy, nurse, bed) and is down for a few hours. She does not sleep through the night yet, she's a booby baby who only eats about 3-4 ounces at a sitting still.
I'm a fan of CIO, but you should really try to tire him out before putting him down, or you'll spend all day trying to get something done around his schedule!
Good luck!