You can buy ovulation thermometers at wal-mart. They cost about 10 dollars. They test your morning temperature. When you are ovulating your temp will rise in the morning but you have to do it as soon as you wake up. Most people also experience increased sexual desire when they are ovulating. That can sometimes be a factor. Als you can check your cervical mucus. When it is stretchy you are ovulating or about to.
Good luck :)