4 negative pregancy tests and 3 skipped periods. What is happening?

I posted a similar question in pregnancy forum, but I thought I want to to focus on women's problems causing amenorrhea (skipped periods) other than pregnancy.

I have no pregnancy symptoms (sore breasts, pain, nausea, nipple darkening), and have had 3 urine tests and 1 blood test. My last episode of unprotected sex was three weeks after my last period. All pregnancy tests were taken at least two weeks after my first skipped period. Have been to a doctor who was of no help. Also have been to three women's clinics for pregnancy tests.

Over 20, so not menopausal. Have not had sex (unprotected or otherwise) since the aforementioned time.

I do no have irregular periods like this, and the last time I was on birth control was over 6 months ago.

I'm not over or underweight, have a normal diet, and not very stressed. No medicines. No diseases I'm aware of. No history.

Would like to if anyone else has had this happen to them, and what it was.

I have never had regular periods. I am now 32. I am used to it. It can be frustrating though. Not having a regular cycle can be scary coz you never know if you are pregnant or not. I have been diagnosed with polycystic ovarian syndrome.

This might be a hormone inbalance. Get a full check up at the ob/gyn including a pap smear and ask to have your hormone levels checked.