It's unlikely you are pregnant. You had two "light" periods. This is a common side effect of Plan B. Your next SEVERAL periods can be early or late and heavier or lighter than normal.
You should also not be using Plan B more than once per cycle. It is a very large dose of hormones and this will increase the severity of the side effects.
Teach your partner how to properly wear a condom. They should not be failing with such regularity. Make sure they are new as well.
You can always take a home test since more than two weeks has passed.