Is there any chance you ovulated earlier? Testing positive 10 days before your missed period seems a bit of a stretch unless you Oed early or were actually pregnant from a previous cycle. In both cases, I would expect a test today to be darker not negative. What brand of test did you use both times? Do you have a picture of the first test? I'm a POAS so I test early, but I don't seriously test (use the more expensive ones/ really look hard) until a minimum of 7 or 8 days past ovulation (which is 5-6 days before my missed period). With implantation and the time it takes for hcg to build up in your system and make it into your urine, a BFP around 4dpo is almost scientifically impossible.
My suggestion is to wait a few days, better if you can wait until your period is due, and test again. In the meanwhile, continue to take care of yourself. You can also explain the situation to your doctor and see if they will run a blood test. Just be sure to ask for a quantitative (specific number). FXed!