The good news is that any doctor can complete hormone screens to check for follicle stimulating hormone to see if you're ovulating. You might want to ask a gynecologist, though...especially if you need your annual check up.
An obstetrician is different than a gynecologist, which is why the OB wouldn't make an appointment with you. Basically, an OB has specialized education and training in the management of pregnancy, labor, post child birth. So she'll only take you if you have a CONFIRMED pregnancy.
A gynecologist treats the health of the female reproductive system, including the diagnosis and treatment of disorders and diseases. Many doctors today have the combined OB/GYN specialty degree. Beware, though: not all OB/GYNs are fertility experts, you need to see a reproductive endocrinologist in the case that you are not ovulating.