Odd period!

Ok so before I had my first child I was regular like clockwork. Every 28 days on the nose. I went back to normal after that and then after I had my second, I still had a monthly period only it would come a day or two early or late or sometimes right on time. Now as I am getting older and a little heavier they are very heavy and very painful usually. Except this month. I had one day of mild cramps and only spotting. I have taken 2 hpt that have been negative. This is the first time it has been so light. I don't remember ever having a period this light before and it kind of scares me since the tests have been negative. Anybody have any suggestions?