Hello. I Just Received Notice That I Tested Positive For

Hello. I just received notice that I tested positive for meth from I m a mouthswab. I do not use the drug so I was very confused. I have before in the past a new times but i am not a user by no means.
I tried to figure out what can cause this because I was told neth is meth on a drug screen bit I read that weilbutrin (bupropion) can cause that and I started that im October aling with taking some Claritin D for my allergies due to the damp weather. Is it possible for a mouth swab to be positive when it should be negative