Waking at 4:30 most nights, possible belly ache?

Im wondering if anyone else has had this issue.
My 9 month old has been a self settler to sleep for ages, which is great. He can mostly self settle for day and night sleeps.
My issue is, approximately 4:30 or 5am he wakes up crying and cant get back to sleep on most nights. Because he self settles I know that its not the issue. He has also been waking at about this time for about 5 months now.
He used to sleep next to us in our room. In this time, I noticed that he sounded like he would want to take a poo, not all nights, but some. He was doing a lot of pebbly poos on and off and I adjusted his food accordingly, and that did work for some time. We had him down to a 5:30am wake up, and we decided to move him out of our room into a room to share with his toddler brother.
Since then though, we have had a series of wake ups on and off at about 5am, which has resulted in a toddle awake and the baby. :o
This morning when he woke up, thinking he was teething, I put him in the pusher, which is kind of in a curved position, and for the first time in months, he has slept past 7am. That said, I have noticed by accident that he actually sleeps longer in this pusher than flat on the bed. He will sleep anything from 1 - 1/12hrs in the morning and approx 45-60min in afternoon in a bed, but, I had to put him in the pusher for 4 days as he screamed like crazy about going in the cot for his afternoon sleep - then he slept for min 60-90min.
Im thinking of putting a pillow or some sort of support under his legs to perhaps relieve any pressure he might have during the night.
Can anyone else advise if they have had the same thing and what did you do.
Right now, Im at a loss as to what else to do.
In addition, he is still breastfed and I am commencing weaing, he also doesn't roll, so he is a back sleeper all night.