Getting discouraged...

Ariel
I got pregnant with my first at 16 after only having sex once. Kept the child and now have a beautiful 5 yr old son. Got pregnant again with my now husband when I only missed 1 week on birth control pills, had an abortion. 
Seemed like I was insanely fertile. Now that we are married and in a place to finally have a baby, it's been 4 months and nothing... Just big fat negatives. 
I'm so discouraged and I don't think that I can deal with it. Why is it that it doesn't happen when you actually want it? 
Anybody else deal with something similar?