I'm sorry you are having a hard time, it is amazing how even if you tell doctors your history they still just prescribe prescribe prescribe. I was literally in the hospital with my leg with a huge abscess from injecting heroin into the muscle of my leg since all my veins were shot..I told them what it was it was so bad I needed surgery and they couldn't wait to give me every pain killer in the book plus they gave me much higher doses then normal since "they knew I had a tolerance". When it comes down to it, it is on us not to ask and if it is pushed on us to absolutely refuse.
A slip and a relapse are the same thing. What matters is that you never give up on yourself and you continue to try to move forward and better yourself. Maybe it is time to put a plan in place for your recovery. That would help a lot to have a back up plan and steps to take if you feel you are slipping. You can do this, it will just take every ounce of your being and then some but it is possible I promise you.
Life is a million times better without drugs, I know it seems impossible right now but it is true. Unfortunately recovery takes a lot of work, but it is worth it in the end.
Selling drugs is continuing the cycle of drug use and addiction. You can't blame this on the pharmacist, you could have corrected them and left with your certain amount, well really you should have torn up that prescription but none of that matters, what matters is what you do now and how you move forward.