Many pups here are on pain meds though 3 weeks, so not too unusual to still need them.

You might try a slow taper off the meds when you think he is ready, that way you can see if he shows signs of discomfort before everything is out of his system.  Some vets don't seem to think this is necessary but I always taper when my dogs have been on pain meds for more than a few days.  Of course keep your vet in the loop. 

I can't remember when Maggie started laying on her amp side (rear amp) but it was probably at least a month or two after surgery.  Eventually she would sit and lay on that side without issue. She even developed a move where she would fall onto her amp side to change directions on slippery floors! I got Elly when she was 2.5 months post amp (also a rear amp) and she was already laying on the amp side.

Karen and the Spirit Pug Girls