My dog is a cavapoo, about a year and a half old, and he was the runt of the litter. He occasionally limps on his back leg, which runs in the family, so we’re not too concerned about that. However, for the last year, he often looks at his behind and runs off to lie down, sometimes jumping up slightly when it happens. It seems like he’s in pain, but he never whines. The vets have no idea what’s wrong, and my mom has spent thousands investigating. He’s had X-rays that showed nothing, and an MRI revealed an infection in his spine and brain fluid, an enlarged lymph node in his iliac region, an enlarged prostate, and an inflamed intestinal wall. He’s been on antibiotics, but the symptoms persist. He regularly has his anal glands expressed, which helps a bit but doesn’t resolve the issue. He’s never eaten much and has little fat. This seems to happen more at night, but it’s hard to tell. Any advice would be amazing. Thanks!
Clearly, he needs a follow-up with the vet. Antibiotics aren’t always a one-trick fix. If he’s still in discomfort, he needs another treatment option.
I had a whippet mix who was afraid of her own farts. She would try to run away from them! Could that be what’s going on?
My poodle does this too! He jumps up and sniffs his farts, then moves away. It’s like he’s scared of them! It’s so funny yet puzzling.
Could there be possible nerve involvement? That might explain the odd behavior.
Poor baby! Farts can be terrifying for them! 
Sounds like he could be experiencing some discomfort from the infection. Maybe consider getting a second opinion from a different vet?
Have they checked for any underlying allergies or gastrointestinal issues? That could explain his discomfort.
Keep an eye on him, especially since it happens more at night. Maybe he’s just more anxious then?
It might be worth discussing pain management options with your vet if he’s still showing signs of discomfort.
I hope you find some answers soon! It’s tough when they can’t tell us what’s wrong.