1st time using bc pills&my period was 3days late& now its very lighter than normal.i last 6days(28days) but now its only 3 .should i be worried?

Periods on BCP's: Today's oral contraceptives are very low dose, so when taking the "sugar pills" (placebo's) in the last seven days of the package, a withdrawal bleeding episode will occur (not actually a "real" period, since ovulation does not occur on bcp therapy). This bleeding may be "light" and may indeed last only three days. To be extra cautious, take the active pill in a new pack on day 5 of the placebos.