Hon, unfortunately it's very common for a woman to get a positive test early and then end up miscarrying mainly because we are able to find out we are pregnant very very early compared to 30 yrs ago.
Approx %50 of pregnancies end in missed miscarriages (where a period is a couple days late) or early miscarriages.BUT sometimes a woman just has unexplained bleeding in early pregnancy and they carry to term.
Take another test in a couple days.
If you got a positive, you need to talk to someone, a parent, an OB, anyone, and determine why you're bleeding. If it's positive, you're pregnant, it's very uncommon to get false positives. If you're miscarrying, you need to see someone, if you don't miscarry completely, and there is anything left over, you can get an infection and it will make you very ill. Sex during pregnancy can be very painful, it always was for me throughout my pregnancy, and so is spotting after, so you may very well still have a healthy baby! Call a doctor and get checked out, good luck!