How can I be charged for drug possession of I didn't have any drugs on me?

I was charged with possession of coacaine and I didn't even have any on me. I was visiting my girlfriend's house and while I was there, police arrived and searched the house. They found cocaine and hydromorphone in the kitchen garbage can and living room area. A CI told the detective that I reside at this house, and I don't, I live at my own home. So how can I be charged with the drug possession when I didn't have any thing on me. The police are also very aware of who this woman is, (the woman's house it was ty that I was dating at the time). Her home has been raided on numerous occasions and she lets people that are buying drugs from her sit at her house and use these drugs.