Is it possible you have miscarried? It is also possible there is a hormonal imballance, or you could be regularly exposed to a dominant female that has your body switching your cycle a little.
Nobody can explain it, but eventually you will all have it at the same time. Women who hang out a lot will usually end up having their periods very close together. It's normal, Don't worry.
Answer...
it depends on how long you've been having your period, in the early years it tends to come unregularly, I have mine for over 8 years now and sometimes I still get it a couple of days earlier, try...
There is nothing "wrong". It is just that your period was light.
Your period is the uterine lining breaking down and bleeding out of your body. It is possible that your hormone levels were low...
No, no period at all is the only indication of pregnancy, because the egg has been fertilized and the uterin lining is retained to support the new fetus