I hope I can help with your question and do message me if you have any queries regarding my answer/advice.
If Simon is bright alert and happy as well as eating and drinking normally with no vomiting or diarrhoea then you could consider watching and waiting for things to improve. However, if the pain is persisting, worsening or frequent then a vet check for peace of mind may not be a bad idea.
These small yorkies are very sensitive and sometimes residual discomfort from injections or rectal examination is left.
If faeces are passing normally and there is no obvious lameness
then I suspect the pain will settle through the day.
However, if new signs develop (sickness, diarrhoea, lethargy, bleeding
bottom, inability to pass a motion) or the pain persists or worsens then pop to your vet.
Good luck and I hope he settles soon
Dr Dan Makin