It could be a chemical pregnancy
. That means you conceived but fertilized egg did not implant. It is very common, just means wasn't a viable egg. Some women will actually start producing HCG
the moment they conceive, others don't until the egg implants. If your body produces HCG straight away you can and will get positive pregnant tests even if no implementation occurred. This is called a chemical pregnancy, not a miscarriage
. In order to miscarry you have to first have implementation.
Check again to see if it is negative now, if it is that means your HCG level is dropping and it was indeed a chemical pregnancy.
But I would still recommend that you see a doctor and get some tests done, that way you can be a 100% sure