What Causes Vaginal Spotting Between Periods?

since some months 3 or 4 drops of blood are seen once in a month and i thought it is of periods.....but den it didn't come....and i consulted the doctor and she suggested for USS...
The findings are 1.uterus is retroverted,shows thick endometrium and a small endometrial polyp..
2.cervex is slightly thickened and shows Nebothian follicles...
3.findings suggestive of mild polycystic disease of the ovaries....
and no problem for any other organs....
actually i didn't understand anything....can any doctors here tell what my problem is....!!!why is such drops of blood coming??
my doctor suggested me Diane 35.....what is it for??
am married...