Can you have a miscarriage and not know it?

Yes: You may have a miscarriage without ever knowing it. You may have a heavier than normal period or some cramping followed by bleeding. Please consult your physician for proper birth control and testing for STD's. Unfortunately I diagnose STD's in young people your age on a regular basis. Please protect yourself from an unplanned pregnancy and a sexually transmitted disease! Good luck.

Absolutely: Absolutely, depending on what you consider a miscarriage. There are many early conceptions that fail quickly even before the first missed period and the next period comes right on time. The only way one would know about this would be to get multiple HCG tests each menstrual cycle - done in clinical research studies, but not very practical in everyday life.