I have been getting that too! But I have missed nearly 4 periods. I only started recently as well.
I have no idea what it is, but i did think that it coul be instead of having a period? I am not sure but it does make sense.
Please contact your OBGYN, irregular periods can be a symptom of many things, one being Polycystic Ovarian Syndrome. It is very important that you have full flow period at least three times a year, and to be aware of what and why your body is doing what it is doing.