How longs it been going on hon. Anything else happen around same time that might have triggered it like a bad dream or has he got teeth coming or having a little growth spurt? C is a cowbag for night crying when her teeth are bugging her and recently had a growth spurt where she was up crying for milk at 3, i gave it her a couple of nights and once the spurt was over she stopped. Otherwise id say same as others. I wouldnt cut nap its counterproductive, C sleeps same hours at night regardless of naps but is grumpy as hell the days she doesnt nap and day after cos of less sleep so for me its pointless to try it.
And same as others have said whats nighttime routine, i bath C pretty much nightly cos it relaxes her and ive banned sponge bob after 6pm cos it winds her back up so after bath its iggle piggle only with a bottle of milk and a couple of organix biscuits which ive found again helps as it stops her getting peckish at night then off to bed with a disney cd
Sorry cant be mor ehelp, nighttimes aint the probs for me, just mornings. Oh edited cos of one more thing, if c wakes really early or in night sometimes its cos her feet are cold. Random i know but just a thought. She sleeps better with socks on