I'm wondering if anyone has had a similar experience with their tripawd post-op or if anyone can tell me if this is just typical behavior or not at the 5-6 day mark?

Long story short, our 75-pound greyhound, Ragnar broke his rear leg back in October. Surgery and treatment didn't work so he went through with amputation last Thursday (6 days ago). The first few days he was home he did great - pain-free, good energy, was already adapting well to walking around, and was comfortable enough to roach several times on his bed each day! Around day 4 he started getting more restless, especially at night, and it's gotten worse to where he's now (on day 6) restless and uncomfortable 80-85% of the day, with some rest in between. 

When I say restless I mean he's panting and breathing heavily and keeps getting up and moving around to different spots in the room like he can't get comfy. His heart rate is not elevated, however, as the vet had me check how many bpm (60). He's also still eating, drinking, going to the bathroom, etc. like normal, and his wound looks to be healing normally without issues. His bruising even looks like it's going down (turning more purple/black and in less area). I just can't tell if he's in pain, reacting to the meds, or if this is just normal anxiety as he adjusts during this time period.

The vet originally told us he should really only be in pain the first few days, so I expected him to start feeling better and heading towards being himself again at this point. Some FB groups have said his surgery meds might be wearing off now so he's feeling more than he did in the beginning.

To give you an idea of his pain management , I'll preface by saying Ragnar has already been on Gabapentin since he first broke his leg in October. We had him on 600mg every 8 hours for a bit, and then weaned off to 600mg every 12 hours. He was also on 75mg of Rimadyl every 12 hours. He's never had any type of reaction like this to those meds before. The vet has him on the same dose now (the Gaba every 8 hours and Rimadyl every 12 hours). I was concerned he might have built up a tolerance and need something else, but the vet advised me that wouldn't be the case. Because of my concerns, the vet also just prescribed an additional med (300mg APAP/Codeine) also to be given every 8 hours along with the others. I started that last night and even staggered them so his pain management would be spread out and it doesn't seem to make much of a difference so far. He will maybe get some relief for an hour before starting back up again with the painting and restlessness. We also tried 200mg Trazodone along with the Gaba the other night and it made 0 difference - he fought right through it. He's also taken the trazadone/gaba combo this before (firework and thunder anxiety) with no issues. 

Can anyone give any advice? Should I try to change up his meds more? Is this concerning? Is this normal and will phase out in a couple more days/weeks? Thank you in advance!