I know this is normal and due to sleep cycles however my 5 month old is desperate for a long morning nap, he takes 3 naps by lunchtime and is only able to stay awake up to an hour between before being cranky and upset that he is still tired.
Do they grow to be able to nap longer naturally or do they need help?
If he is napping next to me on the sofa I can catch him at that 40 minute mark to be able to stroke him when he stirs and help him go back of, but there's seconds in it. If I'm too late he wakes fully and can't go back off at all.
I've also tried wake to sleep but must not be rousing him enough because he still wakes at 40 minutes.
No help, I'm afraid, but bumping as I'm having a similar problem! DS is almost 5 months and just like you I can often get him back to sleep if he's sleeping on me but if he ever naps anywhere else he has no chance of going over 30-40 minutes. Hopefully someone will come along soon with advice for us both!
Someone told me to just leave the baby alone and they'd go back to sleep. I was sceptical but it worked with DD - she'd be awake for 5 mins in the middle of her nap and if I left her alone she'd go back off. She was used to putting herself to sleep already though so I appreciate this won't always work!