Hiya Kim.
You can't half pick 'em girl.
Was Harvey weighed at the vets if not weigh him guessing is no good, learnt this with Oscar some weeks I would swear he had lost lbs.....when in fact he was the same weight. You worry...you guess wrong.
Weigh his carrier then weigh him in carrier divide the carrier from cat and carrier weight .... do not weigh him being held by anyone as people loose and put on weight to
So carrier and cat.
Stick to the same diet.
Question is it possible he is eating elsewhere hence the upset tummy?
Hope it all works out. Sure it will