What is a comfortable amount of exercise to not throw off your cycle but still able to work hard?

I have always been an athlete and my fiance and I are ttc. I've completely stopped working out because I've been so afraid of throwing off my hormones and my ovulation and such. In turn I have gained weight and not happy with myself. But too afraid to work out again because I'm afraid of throwing things off.

What is a comfortable amount of exercise to not throw off your cycle but still able to work hard?

TIA