Nina did something very similar. For the first 4 months she was a great sleeper, in a 12 hour period she'd either sleep through or wake once a night. But then at 4 months she turned into this horror child that kept waking up! At first I put it down to a growth spurt, but then after 7 weeks I decided that enough was enough!!! I started her on solids, once a day, but that didn't really help either.
She's just started waking only twice a night now, from waking every 2 hours. It's now become habit for her to wake at the same time each night for a feed, so I'm trying different techniques to try and stop this.
So really, can't give advice, but can say it sounds pretty normal and hopefully he'll go back to sleeping through again soon.