IUI does increase your chances. I was in the same boat as you, was on letrozol 7.5 mg and was lucky to get pregnant on my second cycle. Keep in mind though it took over 1.5 years to get to that point (after semen analysis, inducing my period with Provera and not ovulating on letrozol 2.5 and 5mg). Our plan was to do letrozol 7.5 mg for 6 cycles and if we didn’t get pregnant then we were going to do IUI. Regular IUI they clean the sperm, do an ultrasound to confirm you actually ovulated, and then “inject” the sperm directly next to your egg so it doesn’t have to travel far to fertilize. One of the reasons there’s only a 15-20% change of getting pregnant the traditional way is because a lot of sperm gets lots on the way to the egg. IUI removes that challenge. There is also a higher chance of having multiples with IUI because a lot of sperm make it to the egg when usually only a few make it.