You have the right to refuse treatment, but if you have PCOS it's not a smart idea. You are 18 and are looking at this with a short-term perspective. You need to look at the long-term risks:
"Having polycystic ovary syndrome makes the following conditions more likely, especially if obesity also is a factor:
* Type 2 diabetes
* High blood pressure
* Cholesterol abnormalities, such as high triglycerides or low high-density lipoprotein (HDL) cholesterol, the so-called "good" cholesterol
* Elevated levels of C-reactive protein, a cardiovascular disease marker
* Metabolic syndrome, a cluster of signs and symptoms that indicate a significantly increased risk of cardiovascular disease
* Nonalcoholic steatohepatitis, a severe liver inflammation caused by fat accumulation in the liver
* Sleep apnea
* Abnormal uterine bleeding
* Cancer of the uterine lining (endometrial cancer), caused by exposure to continuous high levels of estrogen
* Gestational diabetes or pregnancy-induced high blood pressure, if you do become pregnant"
That's very big and very bad list. You should go see your doctor, without your parents, and discuss your condition and current symptoms.