If polycystic ovarian disease is left untreated, will it become worse and do more harm to my body? Tried losing weight but it doesn't help

No harm. Pcos doesn't always need treated. You may have difficulty getting pregnant when you are ready, but it can be treated then.
Depends. Pcos accompanied with a lack of a menstrual cycle may lead to a build up of the uterine lining which may become abnormal over time. Periodic shedding of the uterine lining is a good idea. Loosing weight by sticking with a complex carbohydrate, low glycemic index, diet along with moderate exercising will help you tremendously in the long run. Syndrome x may be a concern as one ages.