Lots of women suffer from secondary infertility (having difficulties conceiving after having had a child).

As someone else mentioned most doctors will not investigate til you've been trying for at least 12 months. You could ask for a CD21 blood test. You go to the doctor on day 21 of your cycle and get a BT done for your hormone levels and it will tell you if you have ovulated or not.

Basically once you do get a gp who is willing to investigate it you will just follow what they suggest and then be referred on to a gyno. The gp may also suggest an ultrasound to rule out problems like fibroids, cysts, pcos, endo etc which can interfere with your fertility.