I feel like I have let my family down

Well, after battling ovarian cancer for almost 3 years and being cancer free for 2 1/2, I really thought that would be my biggest challenge.
But here I am 25 years old and have only had 1 complete pregnancy. I have lost 6 other babies, 1 being a set of twins and it has all happened since Charlie was born.
So, now after trying for another child for so long, I had to finally start fertility testing. I got tested, Tyler got tested, and we are both fine. So, basically I have Unknown Infertility, or Secondary Infertility.
Now I am taking fertility drugs, and this was my first month on them and no such luck. I just don't know how much more I can take.
I mean I am 25 years old! I should be able to spit kids out like a pez dispenser. If nothing happens by the first of the year I will be going to the fertility clinic in Little Rock. I am really hoping that it doesn't get that far.
I feel like I have let down both Tyler and Charlie. Tyler and I have always wanted at least 2 kids and Charlie has been asking to be a big brother for well over a year. And here I can't give them that. What is wrong with me? I mean my doctors all believe that I should still be able to have kids despite the cancer, but for some reasoning it just isn't happening.
So, I figure I will keep going with the meds, and make a decision about the clinic if/when that time comes.
I just hope I haven't gone through all of this for nothing.