After m/c last 4 cycles were regular. i'm 21 and ttc. took 1 test on the due date and another after 4days but neg. now 8days late and no period sign.

It's not easy: Are you having sex on the right days? The test will come back negative on the day of your expected period almost half the time. If after 8 days and still negative then pregnancy is unlikely, but this is dependent as well on your hx of cycles. Did you track the cycles prior to the last 4? Were you on any birth control during that time? Successful pregnancy can take up to a year of trying.