BMI help

So I may be reading too much into this, but I know you have to be a healthy BMI to even be able to conceive, because if you’re underweight your body doesent produce enough hormones. My question is, even though I have a bmi of 17.9 which is in the underweight range, would this still be a contributing factor if this is where I’ve been all my life (except for maybe high school, when I had quite a bit more muscle) and are there other ways to know if my body isn’t producing enough hormones? Just for added info: I have an irregular period maybe once every 6 months - a year. Besides that, mine come the day of or within a few days of my predicted period on glow. However I know just because you have a period doesn’t always mean you ovulate