Could Irregular Periods With Spotting Be Due To The Treatment Of PCOs?

Doctor, I am having PCOS. Feb 2011 onwards am taking metformin. My height is 165cm and weight is 64kgs. I was asked to take syphene for 5 days. But after that my period was missing. After 60 days it came again. I was asked to take letroz also. Then also thought period came on time , it was not very normal. Bleeding was very less. Spotting was there. Is it because of the tablets?