Positive HPT... but I'm on birth control...?

I've been on the Nuva Ring for a month now. When I went to the doctor's I told them that I wanted a morning after pill, and then to inquire about a different method(other than condoms) of birth control. They performed a pregnancy test at that time and it was negative. They gave me the morning after pill, and the Nuva Ring and told me that I could start using the Nuva Ring immediately. They also informed me that it takes a week for the Nuva Ring to kick in. I went home, took the morning after pill, and then started the birth control. I took it out after 3 weeks, as instructed, and my period never came. I finally took a pregnancy test today to rule it out, and it came out positive. I'm so confused. Has this happened to any one else before? Any advice is much appreciated.