OB/GYN specializes in gynecology, and obstetrics which is generally pregnancy and birth, a reproductive endocrinologist (an RE) is someone that specializes in what could be wrong that would make a woman or man infertile. The ob/gyn is the next step in finding out what is going on, as your primary doctor is not specialized, from there your OB/GYN will help you to figure out if you are ovulating or not, or if you have a varying degree of a cycle. From there, you could end up going to a fertility clinic for further testing.