If my bleeding on placebo week is very light compared to usual, could that be implantation bleeding? it's not pink, but it is brown/ red sometimes.

More likely pills : If you're taking your birth control pills correctly you shouldn't have implantation bleeding since the chance that you are pregnant is very low. The low dose pills in use today do not stimulate much growth of the uterine lining and so periods are generally much lighter and commonly become lighter over time as you continue using the pills. Hope this helps.