Still TTC after 8 months

Me and my hubby have been TTC since September of 2015, with no success of getting pregnant, and it's starting to depress me. :( my doctor told me we have to try for a year before I can go in and really start worrying, but I have 2 kids from different relationships, didn't have any trouble getting pregnant with either of them, so I don't know why we're having so much trouble getting pregnant. Any tips? Any advice, all would be great. We've got some ovulation tests, and I have this app, and the Ovia app as well to help me track my periods and see when I should be fertile and ovulate, my husband doesn't have any babies of his own, and we want at least one, if not more. We want a big family, but anyway, is there anything we should be doing that were not? I know we need to have sex a lot more, but other than that, I really don't know. Could it have anything to do with the fact that I work in a casino around smoke all the time, or that I'm about 40 or 50 lbs heavier than I was when I got pregnant the last times. My kids are 8 and 6, so it's been awhile for me. I'm sorry the long post, I just don't know what to do. Any help, advice, and tips would be greatly helpful.