The last time I has sex was in June. With a condom, also plan B pills. I DID get my period that month right when it was due. I also got my period the next two months. But now, I have not gotten it in September, and it's due around this time in October? Any ideas?

Sometimes periods can be very random, depending on how your body is. It also may be because of the type of pill you're using. I'm sure it's nothing but if you're really concerned consult your GP.