Unusually light period??

So my period came on its due date this month (what?! It's never on time haha!) and usually it's pretty light for the first few hours and then it gets quite heavy for the next few days and I always stuggle not to leak at night coz it's that bad (even with maternity pads). 
But this time it's been three days and it's still really light. The blood is a normal reddish pink colour, but there has been no clots and I only had a few mild cramps on day one, whereas I usually am "dying" from pain for the whole week. In fact I can hardly tell I'm on my period right now because it's so light. 
 I know your periods fluctuate throughout the year, but is this too extreme or is it normal?? What could be wrong?