What Causes Irregular Periods After Taking Treatment For PCOD?

i am 22 years old unmarried.i missed my period this month.i have been treated for six months for poly cystic ovarian disease.the treatment was successful resulting in regular periods,reduced ovary size,and absence of cyst.doctor suggested weight loss and a regular use of medicine - glycephage.i am again encountering irregular periods and weight gain.i don't have much weight.approximately 5 kg more than normal and unable to reduce it.i m afraid for my irregular periods.is there a risk of endometrial cancer if left untreated at this stage?or should i again go for the treatment for PCOD?plz doctor help me out