I would be asking them to rule out a blockage x puppies have a tendency to eat all sorts
This was my first thought also Pat - Pearl was almost exactly the same both times she's had blockages
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The first she was very young at 15 weeks and ate a small round of sweet corn cob at a friends BBQ on the Saturday, she was fine until the Tuesday then started with a temperature and was very obviously in pain "passing" broken pieces of the sweetcorn. She had chewed the ring (c 1 cm) into 5 pieces.....I counted 4 over Tuesday / Wednesday but by the Thursday she was becoming increasingly lethargic and had surgery to remove the last piece which was wrapped in bits of sheepskin rug and twigs........
Roll on 3 years and she found a sweetcorn cob at Pistyll Rhaedyr in North Wales on a walk; that was the Saturday, again she was "unwell" from about the Tuesday - high temp, vomitting bile, able to eat and drink but what came out was pretty unpleasant - and likely to be due to gastritis.
Both times it was under a week for symptoms to start. The second time I could have left it for longer before taking her to the vets but having been through the first "sweetcorngate" I was very aware of the risks and didn't want to take any chances, especially, as she is likely to have adhesions following surgery that may prevent transit of foreign objects
Two weeks ago I had a late night dash to the vets for Coral....who had decided to eat a pair of little nylon shoe liners [those tiny stocking things] I could have chosen to let her try to pass them but instead opted to take her for the injection to bring them back up - which she did in a matter of seconds. There were two reasons for taking her - one, I know what it's like to have a dog with a blockage
and two, having read up on the possible effects one of the problems is that the elastic can cause a torsion in the gut - and has very similar symptoms to Oscars - I hope it's not that but did want to mention it in case he's a "sock" theif just as Coral is......
What I would suggest is going back to to the vets and asking about possible gut related issues such as blockages or torsion and see if they can feel anything.
I hope it's nothing more than a viral infection and Oscar is bright and zoomie this morning