Thanks ladies for your replies.

My son then woke up for a feed (at around 6.30) and didn't go to sleep until 20 minutes ago! So that was nearly 3 hours of awake time, and I tried so hard to get him to go to bed, but I think it is gas after all.

I tried putting him down 4 times when he appeared asleep and then he woke up. I was getting really stressed because I didn't know what was wrong with him, then he passed a fair bit of gas, so I am thinking - is this what is keeping him awake?

If so - what causes gas, how can I prevent it, and how do I read the signs that it is gas??

Thanks again!