Femara & Follicle size

I've taken 7.5 mg of femara and on day 18 of my cycle, at yesterday's ultrasound I had one follicle at 14mm, which still isn't big enough to trigger. Just wondering if anyone has gone through difficulty of having bigger follicles grow while even being on femara? What can help follicles grow bigger if I'm usually a late ovulation at day 25? Please help I just want them to grow so I can proceed with my IUI