Period just stopped coming

I've had regular periods for as long as I could remember. The s symptoms were so bad that I got on birth control pills to combat them. I was on them for 4 years. I got off the pills because of the insane headaches I would get and that they could give my a stroke. Which worked or because I wanted to TTC. I didn't have a period for 10 months. I went to the gyno and she said everything looks fine. No PCOS nothing. Then they came back a month after I went to the doctor. I started eating healthier and started to work out a little more than usual recently I order to help my chances of getting pregnant and have a healthy pregnancy. About 4 months after I started to work out my period has disappeared again. I thought I was pregnant but negative tests keep coming. My stress level is the same as usual. I can't figure out why I haven't had my period. Has anyone have any incite of why this could be happening or has this happen to any one else ?