What Causes Delayed Periods With Spotting?

Hi last month i had my period normal. About 10-14 days after i experienced slight spotting for 2 days and now i am late for my period by around 20 days. I am not pregnant i have done many tests but also take extra protection, im not currently on the pill im actually waiting for my period to start it again as i have had my son 8 month ago. is this something to worry about? what can it be?