If you have done it in the past, within a year I wiuld say, and you lose weight, you could come up with a pos u/a. Thc is stored in the fatty cells, and burning fat can release some thc. It happened to my husband after being clean 5-6 months, and getting really sick so that he lost a lot of weight. Try telling this to a po, tho. Either way, ask for a new one soon.
If you had no dope in your system then you need to go to a Dr and explain what happened and take a drug test you will no for sure then. Sometimes mistakes happen.
False positives are more common than one would like to think. Labs make errors. Immediately get a repeat test.
I have a relative that's a cop who this happened to.His repeat test came back negative..but it may be up two years before he gets his job reinstated...beauracracy at it's finest.