Hello there!
Obviously, the biggest thing is, if you're EVER in a position where you think you may need urgent medical attention, it's not a good idea to seek advice on an internet forum. You would be better suited calling your doctor in those kinds of situations, or just heading to an ER.
That being said, I would highly doubt you're overdosing, but you certainly overdid it. If you remain concerned, you need to call your doctor.
Now onto the next concerns. Are you saying your psychiatrist prescribed you an opiate pain killer for anxiety? Or did you tell him you were having some type of pain? Does your doctor know about your addiction history?
It goes without saying that you're on a very slippery slope here. You not only have a history of alcohol abuse (and I'm assuming maybe opiates from what you alluded to?), but also, you have been taking an addictive narcotic to self medicate away your anxiety, and you're taking it inappropriately. That's bad news.
While opiates help an anxious person feel better, it's neither an approved indication for prescribing them, nor is it appropriate, as eventually, with tolerance, dependency and addiction, the very pills that were helping you will end up making your anxiety MUCH much worse, plus then you'll also have new problems to deal with, which would be addiction.
You need to be completely honest with your doctor and with yourself, and get yourself some help for addiction now, before you get in any deeper. We have a wonderful addiction community that I would also recommend you posting in. The folks there are amazing, and they understand addiction, most of them from a first-hand experience. Here's the link to that community:
http://www.medhelp.org/forums/show/77?camp=msc
Very best to you, I hope you find a reasonable treatment plan to address the anxiety.