What Causes One To Have Scanty Periods?

Hi doc I... I m 27 years old and 5.6 in height. My weight is 60 kgs. I have scanty periods.. Got all my hormonal tests done for PCOS and they were normal. Jus that wen I got a TVS done then found one ovary to be polycystic. My doc put me on cabgolin for 3 months to check if my periods get ok but they didn t. They are still scanty . I again went to her so now she put me on blong f , cabgolin 0.25 and oosure plus to make my periods ok. My periods come on time , they are never delayed but just scanty. Pls advise.