That is really interesting - I have the same problem, have for months, and I take Lortab for chronic pain. Hmmm. I never considered the Lortab as a possible cause. I am interested to see what you find out. Good luck!
It could be the Lortab, and some anesthetic agents can also make it difficult to "go" for many hours.
As long as you can empty your bladder, there should be no problems and it should get better in the next couple of days, particularly as you cut down on the Lortab when your pain gets better.
If you feel like you are not emptying, call your surgeon and let them know what's going on.