Urine tests

This is the very reason I'm against testing for pot. It serves no purpose other then to catch people in a gotcha moment. Unlike other drugs and even alcohol, pot sticks around so you don't have to be currently high to test positive. The rest of the drugs have a higher chance of being detected if under the influence at the time of being tested.

Not really sure there is a way around this. You might want to contact a lawyer who is familial with this sort of thing. You can't really prove you hadn't used in quite some time unless they test your hair and most companies will not spring for that level of testing.

That would be my guess.

Exercising will release THC which stores in the fat cells. The first urination in the morning is also likely to blame. It's not a good idea to provide that sample if you have a choice. The collector should have told you how much you needed to supply, which isn't all that much, around 60cc. It's a good idea to allow the first half of you urine stream (where all the nasties reside) to go in the toilet, then capture the necessary amount in the cup before emptying your bladder, and give them no more than what is required.

I am not really sure why this happened. Did you ask the clinic about this?