It sound as though you are either taking to many pills, or you are mixing to many scripts at the same time that are to strong for your stomach. You should let your doctor know what these meds are doing to you. He can adjust, or change your medications. Consulting with your doctor is your best prescription.
You may just be one of those people who can't take opiates. If you aren't getting your hydrocodone from a Pain Management physician, I highly recommend you ask your doc to refer you to one. There are many other things that can be done for pain besides just throwing pills at the problem. Nothing wrong with that if it works and the opiate use is monitored correctly, but there are other palliative measures, such as the TNS unit already suggested, that just might help improve your situation, and in conjunction with the meds you already have on board.
In the meantime, have you asked your doc for a scrip for an anti-nausea drug such as phenergan or compazine? Like your vicodin and muscle relaxants, these drugs can make you very drowsy, so I don't know that I'd recommend trying to use these outside of your home - certainly not until you know of any side effects they might cause with you.
Yup. Get off the opiates. They are inappropriate for long term treatment of back injuries. See your physician about getting a TENS device, and obtaining professionalo medical instruction in how to use it.