Crying before bed

So our bedtime routine consists of bath, lotion, PJS, bottle, books and bed.

Sometimes during the last feed LO falls asleep and for the past couple of nights he falls asleep and wakes up crying very loudly as I’m still holding him (I like to hold him upright for 10 mins so his food goes down lol).

Is he over tired? Does his stomach hurt? Is he having a nightmare? I don’t get it and I hate hearing him cry so much, I have to walk to my room and listen to music. He will eventually settle down and fall asleep but sometimes it takes 20 mins (hubby checks on him every 5).