You might also ask your doc if it's okay to try a small dose of a benzo like diazepam (Valium) or a muscle relaxer like cyclobenzaprine (Flexeril) with a small dose of Norco. For my back, I usually take 5 mg. Norco and 2.5-5 mg. diazepam (depending on how stiff & sore my back is) q. 6-8 hrs., with 500 mg. acetaminophen if there's breakthrough.
You may be unconsciously clenching muscles (esp. jaws) that keep you from relaxing enough to sleep. I learned a creative visualization technique in my Bradley childbirth class that allowed my Halcion (now proven too strong a benzo) to work during the depths of my anxiety-overlay postpartum depression:
1. Gather up as many pillows as you can, and support each limb plus your head with them.
2. Lie down on your back in a dark and quiet room (or put soft ambient music or nature sounds on the stereo or computer--headphones or earbuds might make you tense up). Eliminate distractions--turn the ringer off on your phone and let calls go to voicemail (don't even try to listen to the answering machine or determine who's calling), turn off alert sounds on your computer or mobile device, don't let your pets walk on you, etc.; keep the outside world out.
3. Let your face, neck and jaw muscles relax and allow your eyelids to close (don't squeeze them closed). If it's more relaxing for your eyes to stay open, that's okay too. People fall asleep all the time with eyes open. Let your mouth relax and stay open. The only muscles you should feel working are your heart and those that let you breathe.
4. Imagine yourself in the most tranquil and beautiful place you know: a secluded beach, a lounge chair in a garden, floating on a pond of water lilies, a comfy mattress in a forest, lying on a carpet of thick soft grass at perfect room temperature, etc.
5. Stay limp and let your limbs feel heavy. Do not imagine you need to hold them up--that's what the pillows are for, reassure yourself they will support them. Do not think of results, or worry about anything (especially falling asleep). This is a time to let go.
6. Breathe in deeply and naturally through your nose--the air will pour in like water into the bottom of your diaphragm; breathe out slowly and naturally through your mouth, as your breath pours from your diaphragm. If you find yourself unable to determine when to breathe through your nose vs. your mouth (and don't care), you're on the right track and heading towards sleep.
7. Starting with your feet and going upward, imagine all your limbs falling asleep (not as in "pins & needles") all the way up to your face, neck & jaw.
7. You will probably have fallen asleep by now, and may even be drooling (a sign you're really doing it right). You will probably have started unconsciously thinking stuff that makes no coherent sense, the way you do as you fall into twilight sleep, not quite a dream.
If it doesn't work the first time, lather, rinse, repeat. When my sister fell off a chair in her hotel room (she was trying to change a light bulb, don't ask) I talked her through this as she waited for the paramedics to arrive. I never got to fully use this in childbirth, as my son stopped descending 8 hrs. after I broke water and they had to do a C-section. But it got me easily through each contraction--unnecessary muscle contractions tell your nervous system to "compete" with the only muscles that should be actively contracting. I was disappointed that I wasn't going to be able to continue labor past stage 1, since it felt so soothing to go with the flow!