drug screen

I am a 35 year veteran of nursing. I made a bad judgement while caring for my Mother. I took 40-50 of her xanax. I was turned in by a family member and began the long chain of events to have drug screens done. I have been negative since starting last summer. I went out of the country for 23 days, returned and did a screen the day after I came back. It was positive for benzos. The next screen was negative. I did not take any drugs of any kind other than my scripts. I have searched the internet for help with an explanation and have come up empty. I have been discharged and will have to face the board. Does anyone have any advice or experience with something like this? I am continuing to screen until I hear from the board.
Thanks