Taking 2.5 mg of femara (letrozole) & on cycle day 16 still no follicles. Wht's a normal follicle size and when should they appear? Whn cn I take the hCG shot?

Around 18, midcycle . A mature follicle is around 18 mm but may not release until about 26 mm. It is normal to have a mature follicle somewhere between days 11 and 14 though it can take longer. Your doc will not instruct you to take the HCG until at least one follicle is mature.