I read somewhere that it can take up to six months for you to even ovulate after getting off the pill. And even if you are ovulating and you have sex at the right time, there's still only a 25% chance of conception. So don't be discouraged if this takes a while.
Do yourself a favor and buy some pregnancy tests. Many "signs" of pregnancy are also signs of ovulation, so there's truly no secret, instinctive way of knowing. I had no idea I was pregnant, both times. In fact, on the several occasions since that I have been SURE I was feeling symptoms, I wasn't pregnant at all. And this is coming from someone that HAS been pregnant and knows what to look for.
Follow your periods very closely and remember that they might not be as regular as they used to now that you're off the pill. Use a pregnancy test as soon as you notice that you're late. Sooner if you have money to blow. Also keep in mind that with pregnancy tests, there are plenty of false negatives, but NEVER a false positive. In other words, a negative test is not always accurate and you should re-test if your period continues to be MIA.
But mostly, try not to sweat it. This process is as old as the hills and you WILL get pregnant eventually. The biggest mistake I made initially was trying too hard. Once I relaxed and enjoyed some mindless sex, I got pregnant.
Best of luck to you.