3 month old waking through the night

My three month old who was previously sleeping througjh the night is now waking every one or two hours. I havn't had a decent nights sleep in two weeks and have tried everything I can think of to help him sleep. Has anyone got any suggestions?

He goes off to sleep really well and is always awake when he goes down.

Is he hungry when he wakes up? We just had this with Blake - he went from 5-6 hour stretches back to 3-4 but was hungry every time he woke up. I figured out that because his day sleeps had turned to crap that he was getting overtired during the day and subsequently not feeding well and needing more feeds at night. We've put him back on his 3 hour routine and now using the Baby Whisperer shush/pat technique to get him settled and last night he slept for 7 hours solid.

If he's not hungry, doesn't have wind etc is he waking up at the same time every night? My book suggests gently stirring him an hour before he normally wakes to break his pattern - can't say I've tried this but if it's a habit he's getting into with no reason for waking it might be worth a try maybe? I really hope it gets better for you, I've felt like crap for the last few weeks and when I'm that tired I don't enjoy my time with my little boy which makes me feel even worse.