Hi and thanks for your question,
If you have never had sex (intercourse) before, it is unlikely that you are pregnant. If you are concerned that your "fooling around" may have made this a possibility you could take a pregnancy test to set your mind at ease.
There are other reasons for spotting in the second half of your cycle. It is most likely due to a hormonal imbalance, which can be affected by things like changes in nutrition, stress, activity level and certain medications.
A normal menstrual cycle is 21-35 days long (maybe 5-7 days longer in puberty). The duration of flow is normally 4-6 days long and 78% of blood loss occurs in the first 2 days of menstruation.
If your symptoms continue or your cycle becomes irregular you should see your doctor for an evaluation.