The reason why you have a light period is that you haven’t ovulated. This can happen if you’re stressed or dieting, for example. It’s also normal for your period to change a couple of times over the course of the year for no reason at all.
The last two times I had my period, I bled very lightly indeed. I haven’t needed to use a towel – just a pantyliner now and then. Is this normal? I’ve had my periods now for 2 ½ years.