You can get a blood test at a doctor office to make sure and also find out what is going on with your period.
I went to the doctor on Friday. We've been trying for 7 months and this last month we used an ovulation kit. I tested negative at home with an EPT test but had a faint positive at the doctors office with their urine test. Doctors tests are a lot more sensitive than the home ones. I'd make an appointment!
I was 3 weeks late after never being late a day in my life!! I got my period that third week but got pregnant after that cycle! A blood test may be needed for you!!