My husband and I tried for 5 years before my son was born. I was definitely on the heavy side. We were going to Jamaica and so I went on a 'fad' diet and lost about 30 pounds - and got pregnant 2 months later. I do think that weight can play with your periods and hormones in general. Mine have always been a bit on the erratic side and it was not unusual for me to also go anywhere from 3-6 months between cycles.
A few years later we decided to try for our second as well (5 years actually!). By this time I was not only diabetic but also had high blood pressure - both items I still try to control by both medicine and a healthier life style. The insulin issues with diabetes are really just hormone issues. The medicines I was taking were hormone inhancers, so they helped ALL my hormones, not just insulin production. In fact, what I was taking said very explicitly on the bottle that it increased the chances of pregnancy. And it did. I was pregnant in about 3 months. Turns out they actually used the same medicine sometimes as a fertility drug.
So if you are taking medication for your insulin, you may want to talk to your doctor about alternatives that may boost other hormones as well. I was taking Avandia, and while it certainly helped both with the pregnancy issue and the diabetes issue, I am not sure I would recommend it. First, you have to stop taking it immediately upon getting pregnant because it can cause some complications. I was probably about 5 weeks along when I realized and had to switch to something else. Second, there have been some medical side effects that have popped up recently (maybe liver damage? I'm not sure) from long term use of Avandia.
But definitely speak with your doctor about what you are taking and what you may be able to switch to. I have been exactly where you are, and it gets better. I promise!
Good Luck!