There are a lot of symptons, but depending on the severity depends on how many you get.
From personal experience my periods were always pretty scanty and as time went on (and the severity of my PCOS) i was only having periods 2/3 times a year.
I also started to put on weight in my early 20's for no real apparent reason. I wasnt a big eater but the condition sometimes grabs at any fats / sugars that are around and holds on tight to them hence making you put on weight. I also started to get facial hair which totally freaked me out - its common to get it on your back, neck, arms too which i didnt have. I ended up having electrolis which cost me a fortune.
Like i have said this is only my own personal symptons. THere are many - look it up on google.
I was only diagnosed when after about a year of trying and went to the fertility clinic although i had read about it previously and did have my suspicions. My consultant done an internal scan and looked at my ovaries and it was as clear as day that i had it severely - my ovaries were like a couple of golf balls - massively pitted. Fortunately for me and year or so later i had surgery where the consultant blasted my ovaries so that i could fall pregnant. Apparently you carry the condition with you through out your menstral years and as time goes by the condition worsens. Many women are not even aware they have it at all. Hope this helps.