Can still be pregnant for having heavy periods for 4 days?

The best sign of being pregnant is missing periods. There are some pregnancies where the woman will bleed through out and those can be mistaken for periods, but they're usually not really heavy.

Why do you believe that you're pregnant?

If you are pregnant, the bleeding should be reported to your doctor or midwife. If you have been trying to become pregnant, but are now having a heavy period, it is likely that you are not pregnant.