Pain and discomfort when masturbating?

[ex-swaggerd.livejournal.com]

For the past week and a half I have been experiencing a bit of pain and discomfort when I masturbate. I only do so clitorally so I don't think it is an issue with my actual vagina and it's only when I am aroused. I am 21 years old and am a virgin and that isn't likely to change in the near or distant future. I would really like to not go to the gyno because my entrance is so tight that anything beyond the size of a finger would be excruciating. So should I be worried or is there a certain amount of time that I should allow it to go away before going to the doctor?

ETA: I should be starting my period soon so could this just be a symptom?