Bless him, your photos brought back some memories, my Bella had LP surgery in June this year. The bowel and bladder can be a little sleepy after a general anaesthetic and that will be why he's not been potty as often, has he been at all post op ? Your vet should have made sure he'd peed at least once before they discharged him, I would ring and ask, if he went at the vets you can prob relax a little and wait for nature, just make sure his tummy is soft and not getting distended. If I remember rightly it took about 2-3 days for Bella to poop but she did wee straight away. Good luck.
Willow, Bella & Alfie