If youre taking certain (off-topic) drugs during the course of your Pain Managment program, that will affect it a bit and certainly your metabolism. Losing weight will release THC from fat cells in urine!

Burnt Toast has already given advice to not try to lose wt. while trying to pass a test (in so many words). Even though it is something that will be helpful for your health.

Sounds like you need a good replacement plan for urine as previously suggested! I'd invest in replacement pee, many threads of the same. Good Luck! PR