Pregnant and Addicted!

So I have had problems with addiction to street drugs since I was 14. At the age of 18 I was finally able to get clean from Meth and now I am 26 and have not touched street drugs since.
The problem is I have had problems with script pain meds off and on for as long as I can remember. I am an addict and of course will be for the rest of my life, whether I am a clean addict, or a practicing addict, I understand that addiction is something I will struggle with my entire life.
I have a disease that causes severe chronic pain and among many other treatments one of the thing DR.'s always seem to fall back to is pain meds.
I previously was taking Tramadol for a while and was doing great on it. It worked really good and did not have the addiction and withdrawal problems as narcotics.
Then I found out I was pregnant and Tramadol is a pregnancy Category X so I was immediatly taken off of it. The Dr put me on Oxycodone as it is really the only pain medicine that is category B, most are C or higher.
Than problem is I am not seeing that I have become addicted to them. I am taking 15 mg's every 4 hours, adn sometimes I even get up in the middle of the night to take them.
I am now 4 months pregnant and want to stop taking them so bad. I know I will be in pain when I stop, but in all honesty, I am in pain even with the meds. The disease I have is in my bladder and of course the further along I get it the pregnancy the bigger the baby gets, and the more pressure on my bladder, thus more pain.
I would stop cold turkey but I know that it is not safe for the baby. I know I need to tapper off but to be honest I dont know how to tapper. In the past I have always quit old turkey, even from the meth, so this is the first time a tapper is needed to make sure the baby is ok throughout the process.
If anyone can help with suggestions for tappering off I would so much appreciate it.
Also, please know that I do not take the medication more then it is perscribed, and I have a very real disease that causes very severe pain. I dont need to be judged, I am here for help. My Dr only says that this much med is not good for the baby and then hands me another script, he wont help me tapper down, so I am on my own.
Please help!!

You need to get on Methadone and quick. It's safe for the baby and will help with the pain much better than the oxycodone. You risk a miscarrage if you try and withdrawl during pregnancy.