I tried him with the pepti jr and he point blank refused to take it.
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Yes, he was 10 weeks when this started.
He has been on it over 4 weeks now, and this is the first time we've had this kind of behaviour without reason - one time was because I forgot just one dose of Gaviscon in his feed. The other was down to developmental leaps.
I suppose this could be another leap? He's desperately trying to roll front to back, as he frequently gets stuck like a turtle on its back. Except he is on his front. 
Ah, actually, I don't think it is a leap, because today he has only rolled twice (previous 2 days he has rolled easily 50 times or more), and I am fairly sure he has not wanted to because it must hurt lying on his tummy.
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We should be back to see the consultant in a week or two, so I will go over things with her then.