Peggy, I have just read a little about oxynorm and I think you should phone the doctor who prescribed this for you.
I've had a short read about this drug and I'd recommend speaking to GP.
I understand it is prescribed for pain relief. Many people who are hypothyroid and on levothyroxine suffer from pain but it's usually due to being underdosed or levo doesn't suit them. Sometimes the addition of T3 helps with pain as it is the Active hormone required in our cells. T4 (levo) should convert if you're on sufficient.
There's no thyroid history in your Profile so I don't know whether or what you've been diagnosed hyper/hypo - dose.