There are so many things that could be causing this it's impossible for anybody on a forum to say for sure. I would first take him to the GP just to rule out reflux, allergies or other issues that could be causing the sleep disturbances. Then try sleep school or even some sort of in home sleep consultant like night nannies for example (we used them and they are amazing! They don't advocate leaving baby to cry so you don't have to worry about that). And there is nothing wrong with co-sleeping if that works for you.