I’m 18 and my periods are still irregular. Should I be worried?

I’ve had my periods since I was 11 and now I’m 18 and they’re still irregular. I’m not sexually active or overweight but I do have a thyroid problem that I’m on medication for, that is working. But my periods are anywhere from 28-40 days apart... I’m not sure when I should be concerned and talk to my doctor about this. Any advice would be helpful.