There is virtually no way you can get pregnant, taking the precautions you do. You need to relax and enjoy sex a bit more!
Some women get very light periods while on the Pill and some end up with none at all. The longer you are on it, the more likely you are to have very light periods.
A pregnancy test will ease you mind. A bit of anxiety is normal but keep taking your pills as prescribed and trust yourself and your birth control!