When I miscarried at 10 weeks along I had a positive for 2 months after having a d&c. The only way to know for sure if you miscarried is to get a sonogram. They would look for a heartbeat and make sure baby is measuring correct and not behind.
i agree with coffeebuzedliz
and if you are taking a test because you want to know if you M/C, a home pregnancy test is not going to be the most accurate and you should go to your Dr. and ask them.
If you just M/C then yes, it can take up to a couple of weeks for your body to return to normal and for the HCG in your system to decrease to zero where you wont get a positive test. Its better not to take a pregnancy test right after because its likely false and women will get confused that they are still pregnant even though they have had a diagnosed M/C.