4 month old waking every hour!?

My son will be 4 months next week. When he turned 3 months he started to wake up quite a few times during the night. Before he used to sleep for 6-8 hours a night. Last night (and he's done this other nights too) he woke up EVERY hour. I try to calm him by rocking him or patting him but it doesn't do anything. Instead he cries more (though his eyes are closed). The only thing to get him back to sleep is to nurse him. So I'm literally nursing him every hour. I'm sure he's not actually eating each time but that's the only thing that seems to get him back to sleep. The pacifier just doesn't get it. I'm back at work so this is really tiring and I need a solution for getting him to sleep throughout the night. He is a co-sleeper and I'm not sure if this is the problem but I need to know of any solutions out there. Also trying to let him "cry it out" doesn't work, he'll just cry harder and longer...TRUST ME!