A month ago I had my reg cycle. Two weeks later I had light bleeding for a day and a half. And then started my cycle again today (the 28th) which is on time. What could this mean?

Occasional spotting or light bleeding can happen for a number of possible reasons. It may have been due to ovulation, may be an unexplained shift in hormones, may be due to hormonal birth control if that is a consideration, etc. Many women will experience it; sometimes just once that they can recall, sometimes a few cycles a year, sometimes on a regular basis. In most cases it is a one off and not a cause for concern.

If it were to continue fairly regularly for you; for example over the next few cycles, since it is a new change, it would warrant asking your doctor about it.