Heavy and irregular menstruation which started late (about age 14). Blood could soak through heavy-duty pads and tampons in a few hours, and there was always a high volume of clots that came with it. It usually came around once every 3-4 months, but what brought me to the endocrinologist for PCOS initially was that I had a period that wouldn't stop for more a whole month. They put me on birth control to regulate it.
Blood sugar abnormalities. It basically makes it very easy to develop diabetes and gain weight, and difficult to lose weight. I was 250 lbs by the time I was 15. I had pre-diabetes for a while in my early 20's, which stained areas of my skin with a kind of brown/dark color (back of neck, inner thighs, below breasts). I was put on metformin for it, couldn't get myself to swallow the pills, and focused on diet instead. This cleared the stains and stopped the rapid weight gain, but did not seem to help with weight loss.
High blood pressure and cholesterol. These are common issues for young women with PCOS. I received meds for those too, which I went off of because the cholesterol pill seemed to be causing side-effects and the blood pressure pill didn't seem to help. These values have normalized as I've gotten older, which is probably down to menopause / decreasing hormone levels (I'm in my early 40's).
Hair and skin was mainly acne, facial hair, thick body hair, and hair loss. I didn't have extra hair on my chest or back, but I recall the endocrinologist saying that was a common trait of the condition.