L have poly ovarian sandromes and my doctor gave me diane35 pills but it may cause gain weight is there alternative and I am still breastfeeding?

Maybe. All bithcontrol mdication may cause some weight gain. If you are able consider metformin to counter the Insulin resistant syndrome in pcod and addiing this may help weight loss.
Weight gain and OCP. Birth control prills contain estrogen and progesterone-like chemicals. Estrogen does not cause weight gain but progesterone-like medication does. The worst problems with weight gain occur with depo-provera shots usually given every three months.