A plea for help!

Can anyone tell me why our son hates going to bed so much? He cries... Every, Single, Night!

He's only four and a half months and we try hard to give him a nice "wind down" before bedtime, but despite this he wails every night. Often he just refuses to be put down into the cot and cries to be held and for the lights to be put back on. It doesn't matter whether he's tired or not, he will still complain. It's like he has learned to hate his bedtime. Is this possible? Can anyone tell me what might help, please?!

It's been like this for perhaps a month, maybe longer (it feels MUCH longer) and it is really starting to get to me down. Last night our entire evening was made up of getting him to go to sleep.

So if anyone has any pearls of wisdom, please share them here.