Rreally, I agree with Rose Red. I once came up positive on a test and I insisted on a retest. The company just let the matter drop in my case.
But, failing that, you have already admitted you screwed up. Now it's time to fix things and get another job. Was this just internal to the company, or did they report you to the D.O.T.? If they reported you, you should fight this while you're looking for a new job. Is your license still intact, or do you have to change professions? It's ice cream season and the chances of getting a driving job tomorrow is good if you hustle. All you need is a chauffeurs license for those trucks. Landscapers may still be hiring, and that's another immediate job.
Get a job, any job, while you're trying to straighten out the mess you got yourself into. It will make getting a good job easier, and help pay some of the bills.
I'm sorry to hear about your troubles. It's pretty stupid that pot is as illegal as it is, when truckers taking speed, drinking, and missing sleep are the real dangers.
Hopefully you will bounce back soon and get things under control again.