My question involves criminal law for the state of: MI

Part two of my crazy story... protected GF with DV charge against me slipped a shared bottle of illicit adderall we both shared for studying purposes at University into my backpack, and told the police. Police were somehow able to obtain a search warrant for our shared apartment and my backpack and found the bottle of adderall inside my backpack... while i was in pre-trial jail for the DV charge. I got popped for felony possession. They didn't conduct fingerprint analysis on the bottle or anything.

Question is... how exactly is this constructive possession, if I was actually banned from the apartment via restraining order at the time of the warrant and in fact in jail? And... anyone could have put anything they wanted inside of my backpack to nail me for anything? Just like my GF did...

Is there any possible legal defense here?

Thanks for your time.