You are correct to be concerned, as a violation of this condition (the drug testing) by having a positive test result could be a basis for violation of probation. You and your lawyer should have brought this up during the hearing when the Judge gave you the sentence, and let the Judge decide this issue at that time. Explain the situation to your PO, ask whether this condition can be waived without you needing to go back to the Judge, and if not, contact your lawyer about filing a Motion to amend the conditions of probation. Good luck.
DISCLAIMER I do not practice law in your State. This answer is provided for informational purposes only. This answer does not constitute legal advice, create an attorney-client relationship, or constitute attorney advertising.
I agree with Howard's answer. It really should have been dealt with at the sentencing, however since you are in the situation now, you should address it with probation or the Judge. I can help you with this matter. Visit me at www.kliszlaw.com to discuss. Tim Klisz