the local clinic said it pregnant but the first response home test says negative?

Hello all. I went to my local clinic for my Nexplanon insertion. I go there, wait 3 hours, for them to tell me my pregnancy test came back as a "faint positive". I was so shocked. Me and my boyfriend went to the store to buy tests at rite aid. We bought two boxes. One box was first response and the other the rite aid brand. I took one. The first response is a negative so I'm not sure how they even got positive. Not sure what to do now