Why GonalF and Femara??

I am very confused. I have taken letrozole and produced 2 very mature follicles each month the last 2 months. So 4 eggs, TI, no pregnancy. I have PCOS and am on Metformin. My RE stated if we wanted we could do Letrozole and GonalF (small dose) and our 1st <a href="https://glowing.com/glow-fertility-program">iui</a> this month. She explained that due to age (34) and still trying to have our first baby that injectibles help increase success rates. I agreed and my meds are ordered, but I realized later that GonalF does the SAME THING as Letrozole. We obviously don't want more than 2 eggs because that could lead to a cancelled round of <a href="https://glowing.com/glow-fertility-program">IUI</a>. So why on earth would she suggest GonalF if I was already responding to Letrozole well the last 2 months?? I'm nervous, will I likely over stim? I don't have an ultrasound until Monday.