Losing weight is one of the best things you can do not only for your body but in preparation for pregnancy. Even losing 10 lbs is super beneficial! Anyway what you need to do is find out when you are ovulating. I personally do not like the OPKs (ovulation predictor kits) as there are too many variables and problems that women have with them, plus they cost money.
I would either buy or find this book at the library: Understanding Your Fertility. It outlines how to know when you are ovulating and just a lot of information about your cycles and reproduction in general.
The tried-and-true method of my choice is monitoring cervical discharge. Did you know that for the majority of her cycle a woman is infertile and for a small window (about 48 hours or less) she is fertile. A woman is fertile when the mature egg bursts from the ovary and begins traveling down the fallopian tube, ready to meet with a sperm for fertilization.
Before and after ovulation your cervix acts like a castle wall, blocking at sperm. But as your body prepares to ovulate and does ovulate the cervix thins out, opening up for the sperm, and as a result you will have a discharge. You may notice it when you use the restroom; it can be slimy, sticky, stretchy, clear, cloudy or yellowish in color. When your cervical mucous (CM for short) is clear and stretchy (stretches to over an inch) you are at your most fertile and should have sex.
Good luck!
I would try ovulation predictor kits so you know if you are ovulating or not and to when. Some people chart and use BBT but I never did, wasnt that patient. You can also use your bodys natural signs such as ovulation pain, cervical position, and cervical mucus to know when you are ovulating as well. If you are unsucessfully TTC for a year, that would be a good time to see a dr. I was 35 when we began ttc #3 and it took us over a year but I had to have medical intervention to finally get us pg. Good luck to you.