Is it possible that you're pregnant? During pregnancy it is possible to spot a little or even have period like bleeding. Or are you on a low hormone birth control? Sometimes a lower hormone bc can cause spotting in between periods. Either way it's unusual and you probably should see a doctor. If you aren't pregnant you really shouldn't be spotting in between periods or missing them. If you are pregnant, you really shouldn't be spotting at all.
Is it spotting or actual bleeding?