The menstrual cycle is typically 28 days but that is not an absolute rule. Different people have cycles that last different lengths of time. Yours was just shy of 28 days, and there is nothing to worry about. Lots of things can affect the cycle -- stress, diet, weight gain/loss, etc.
Sounds like you are just having a blip in your cycle. Do you normally have regular cycles? Also have you recently changed your diet or have you been under any stress?
Are you taking birth control?