Will the pill be ineffective?

You have many fears, but they are all unfounded. Your body doesn't "get used to" birth control pills so they no longer work. Birth control pills have been used for over 50 years without this ever happening, so don't worry that it will happen. I know it's hard to believe that this one little pill could have such a huge and important effect as to prevent pregnancy, but truly, it does. The failure rate among women who take the pill as directed is basically nil. And once you've been on the pill for a few months, like 3 or 4, your ovaries will be suppressed and it will likely take them a short while to restart. The only thing that could be a problem is that some antibiotics interfere with the efficacy of the pill, as does the supplement St. John's Wort. So don't take those while using the pill.