Doubling condoms works against you, they tare. Also you should not be just taking the pill "sometimes". Go to planned parent hood and get a test and also get some info on sexual education.
First, stop doubling up on condoms. This makes them more likely to break because of the increased friction of the latex. Use one condom and take birth control to best guard against pregnancy.
If you didn't notice a tear in the condom it is unlikely you are pregnant. But take a test to be sure.
Stress, diet change, exercise, and illness can cause you to miss your period. If you don't get your period soon and the pregnancy test is negative, see a doctor to rule out other health conditions.