My DD had similar problems at this age and I found sitting her on a potty really helped. I think the different position helped to move things through.
I guess don't do banana again for a while? I took it as a sign that DD wasn't really ready to eat much and didn't let her have as much for a time. She was very keen, but actually a bit late to get going with food - her enthusiasm exceeded her capacity It was suggested to me to try pro-biotics, though I never really figured out how to get her to take them
Hope he's doing better soon.
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