You are not in danger of becoming "addicted"! You are not abusing the medicine, to become an addict you need to also be an abuser.
There is a difference between addiction and dependence. When you are a long term user of pain meds, you become dependent on them and you may have some withdrawl symptoms if you stop suddenly. Should you and your doctor decide that you are no longer in need of medicine, he/she will come up with a plan to titrate you off of the opiate based meds so you encounter as little withdrawl as possible.
As far as taking pain meds, you are on such a miniscule amount of pain medicine that you really have little to worry about.
If the t4 is working, you are in a great position, because as far as chronic pain management goes, many of us pain sufferers are on much higher and much more frequent doses.
Don't be worried you are not in danger,
brian