How old are you, and how long have you had periods for??
Are you usually regular??
It just sounds like a funny cycle to me, which lots of people have a lot, maybe it's just an unusually light period and nothing to worry about??
If you've been having regular and even periods for a while and this is totally out of the blue ask your Dr, and they can do a blood test and check that your hormones and stuff are OK. It could be a number of things and it could be nothing but best to be safe I suppose??