No periods, advice?

So I've always had irregular periods I can go anywhere between 2 weeks and a year between periods. I am extremely worried that I won't be able to conceive. I've been to the docs the past year every 3 months for bloods for thyroid issues but it's always borderline so he just says to go back again in 3 months for another thyroid check. I'm getting impatient with the 3 monthly checks now. Any advice?