That test they are referring to--
 

--is a nerve conduction study and electromyography (EMG). The first part of the test involves the placing of electrodes measuring the sped and quality of your sensory nerve responses, and the EMG involves inserting small needles into the muscles to measure the quality and speed of your motor nerve responses.

Given that you've had spinal problems, I'm surprised you haven't had this test before--it's fairly common when people present with neurologic symptoms, and can often help determine just where the nerve dysfunction is--peripheral vs. spinal cord/nerve root, if done at various places. The problem is that it only can measure gross dysfunction of larger, myelinated nerves. It is also possible for one to have dysfunction of the smaller, unmyelinated nerves that subsume the sensations of pain and temperature. These are too small to be captured by nerve conduction of EMG studies, and often need more specialized testing, including qualitative sensory testing and/or skin biopsy to look at intraepidermal nerve fiber density and condition.

Overall, given that you say you're diabetic, you may be co-morbid--that is, have more than one thing going on. You may have damage to the spine and nerve roots AND also to more peripheral nerves as well. It is notoriously difficult to tease out the causes of neurologic symptoms--the same symptoms can come from damage to the brain, the spinal cord, or nerves farther down. Also, people with multiple conditions often have what is known as "double-crush phenomenon"--nerves already compromised by one problem, say spinal compression, are then affected biochemically by something like diabetes and produce symptoms that are more than the some of their parts. (Diabetics are well known to suffer more symptoms from spinal compression than non-diabetics--their nerves are already compromised and it takes less mechanical compression to set them off.)

It sounds like you are at a fairly early point, unfortunately, in teasing out what is going on and what can be done about it. It is fairly standard for non-opiate medications, especially anti-epileptics such as neurontin or anti-depressants such as elavil to be prescribed for those experiencing nerve pain as opposed to nociceptive pain (the distinction is the latter comes from normally functioning nerves recording damage to other tissue, whereas the former comes from actual damage to nerves, and is often described as oddly burning, lancing, electrical, or involving sensations that have no obvious origin). But you may need more a more thorough work-up, along the lines of the testing protocols of the Liza Jane spreadsheets:

www.lizajane.org

As Ginnie said, your dosage of three a day is not very much at all. You may well need something else in the mix.
You will have to keep better track of your medications to know exactly what you had a weird reaction to. Morphine causes itching, but that it about it usually. Methadone is extremely effective for nerve pain, but has more side effects. What you are currently taking is not time release. There is a time release version, OxyContin, but it has been reformulated because of all the abuse and is rarely prescribed these days. MS Contin is time release morphine, it would help if we knew what you had taken.
Gabapentin, or neurontin, is the standard first line medication for neuropathy. It is an anti-convulsive that calms the nerve endings, and works for some patients. It does help me, but not with the major leg pain, just the burning in the feet. Many, if not most, of the people here have experience with it, or the newer version, Lyrica. They are very similar, but some people do well on one but not the other.

I was also offered a spinal tap, but my neuro at Hopkins was offering it like a waiter offers dessert, he didn't expect me to take him up on it, and wasn't surprised when I didn't.

If a cause can be found, of course you should pursue it, but please research this site. There is so much information here, and you will see that sometimes there is only palliative care and a definitive diagnosis can be elusive. I know what I do about pain medication because it is all that can be done in my case. Hope for a treatable cause, never trust just one doctor unless you have a long and satisfactory relationship of mutual respect, but sometimes you do have to accept things the way they are. I am only a few years older than you. I do not think I am in as much pain, but my condition is progressive. This site represents a lot of collective wisdom and some very thorough research from a wide variety of PNers.

Hope that you get relief ( and a treatable diagnosis) soon!
Glenn's response is very valuable. He is extremely well informed on the subject, much more comprehensively than myself.