How do I know when I ovulated if I have a period every two weeks

You have to track your temperature for several months. By taking it daily and writing it own on a calendar, you can see when a pattern develops.

Some women experience a small amount of spotting when they ovulate. Usually it is so slight that it is easily overlooked. But keeping track of your temperature is more reliable.

If you are having an actual period (or heavy bleeding) every two weeks, you need to see your doctor. Something is wrong.