i'm inclined to agree with MadB on tracking sleep. my DS was never a great sleeper (and still doesn't 'sleep through' at 2) & (with the benefit of hindisght) i can say that DS changed numerous times - just when i'd think we had some sort of pattern to follow, he'd change - right down to how i would actually be able to get him to sleep. i think around 4 months is notorious for wake-ups & alot of people talk about the 4 month sleep regression.

i remember at about 4 months just giving in & going along with the flow - DS would only sleep on me for naps in the afternoon so we would nap together on the couch. not ideal, but i felt a lot better once i stopped fighting it! by 6-7 months his naps were better & i wasn't napping with him anymore.

fwiw, i don't think you're doing or have done anything to mess up his sleep - he's just being a normal baby! chances are he'll continue to change - but i promise that they do seem to become more predictable!

it is tough when they're waking frequently....so make sure you're getting some down time & 'me' time when you can to recharge your batteries.