It's been a year and still nothing

My husband and I have two amazing kids 4&7 and we have actively been trying to conceive since last May. I'm an only child and have always wanted a big family and with both my other pregnancies we got pregnant right away . I am now 27 and he's 30 and I'm starting to get irregular periods. My doctor chalks it up to weight gain and although I have gained some weight it's less than 50 pounds . I always had semi irregular periods in the sense that I couldn't pin point it to a specific day however I have now been skipping periods so much so that last October they put me on a pill to help jump start them and so I take those and get a period but still nothing. The more time that passes the more discouraged I get about having a 3rd. We had our first child when I was only 19 and so I've always said I wanted to be done having kids by 30 but now that we are trying for at least one more it seems like that might not happen. I've never really talked about this struggle before so Im just now venting about it .