how did you find out you had pcos

hi there! I'm relatively new to ttc. were on our third month. I was on birth control for 3 years and stopped three months ago. I had two periods which were normal but now I'm 9 days late, but all my pregnancy tests have been negative. before I went on birth control my periods were super irregular. I guess I'm just wonder how you'd be diagnosed with pcos, I don't know a whole lot about it. but I'm worried if I'm not pregnant and I'm not getting my period that I'm also not ovulating. just looking for any advice you guys might have. thanks!!