S.P.
Has it gotten cooler at night? Could he be waking up because he's cold?
I had that happen with my son and my god-son. A warmer onesy and turning on the heater was our solution. Is he teething? Another question is if you tried letting him CIO when he wakes up at night? I understand the need for others to sleep but if he figured out that you come running every time he fusses, that's your problem! You know how smart they are! ;)
So what happens during nap time? I've had days when my son's naps were off but he would still go into the crib and stay there for at least 30mins even if he didn't nap, it was enough down time for him to wind down and not have it effect his night time sleep.