Tested possitive for amphetamines

I recently submitted to a sliva test as part of a pre-employment drug screen, and it came back positive for amphetamines, which I have never used, illicitly or otherwise. I was informed that it is possible that this may be an indication of the onset of type II diabetes. Is there any credence to this claim? I am a 44 yr. old male and have enjoyed good health my entire life. There is no known history of diabetes in my family, although in the last year I have begun to experience other symptoms such as an increase in the frequency of urination, night urination, and the need to wear reading glasses. Also my weight has crept up to where I am currently border line overweight. Also, I sell plasma regularly. Could this account for my possitive drug test? I don't do drugs. Really...honest...I don't.