Need some advice.......struggling

Ladies.....I suffered a missed miscarriage the week of thanksgiving. Have been checking my hcg since then and it was back down to a 3 on the 12th. I had it checked on the 12th because I took a hpt and it was positive. How in the world can a pregnancy test pick up a hcg level of 3? My doctor thinks it’s just a fluke but still today 5 days later I got a faint positive. My hcg should have been gone 5 days later. I just don’t know what to think and it’s so frustrating because I’m ready to try again.