Extremely light periods for three months. blood stays nside vagina. negative hpts. any ideas?

Sounds ok : If your menstrual cycles are still coming once a month then most likely this is just a normal period. There's nothing wrong with having a short light menstrual cycle. People who have heavy cycles would likely trade places with you. if you are concerned about your menstrual cycle consider seeing an OB/GYN doctor. They can discuss options for menstrual cycle regulation