Emily, it is normal to test for pregnancy once your period is officially late, and then repeat it 7 days later to confirm the result. Use an early detection kit like First Response Early Result (not the digital one) which is the most sensitive test on the market.
Missing 2 pills in the 3rd week will more likely than not mess up the cycle.
You should just keep on taking the pills, one after the other, one pack after the other regardless of what your bleeding or not. You should never adjust the pills you are taking to what is happening with your cycle. Your body will adjust to the pills.
Of course any time that you miss 2 pills and have unprotected intercourse within 7 days of that, you stand a chance of getting pregnant. The chance is however relatively small compared to when you are not taking the pill. It is however not 0%.
It is also important to relax and not stress. Stressing can not make any difference to the outcome so it has no use at all. It is however poison to your system and health and it will mess with your cycle.
Best of luck!!