What Causes Lack Of Ovulation Even After Taking HCG Injection?

we are under ttc for 2 nearly years....this month...i underwent follicular study...and today is my 15th day..and my study showed that i had 2 follicles on my left ovary each measuring 2 x 1.75 ....i was given hcg injection on day 13th when my follicle measured around 1.8 x 1.7....i haven't ovulated yet....Can u pls advice me what to do