Sterile or just incredibly lucky??

I've been with my boyfriend for almost 3 years now and in those span of 3 years, we have never used any form of protection except the withdrawl method. The WITHDRAWL METHOD. Which I completely understand is the worst form of BC. I have friends who did the same thing I did and got pregnant in within a year. The thing is, I have hemolytic anemia, a genetic mutation which causes my blood cells to die faster than an average person. I also have medical conditions with my liver and other sorts of complications. Could it be that my medical condition causes my body to reject fertilization because it will not be able to conceive and support it, or am I really just a lucky person who's boyfriend is amazing at what he does?