I've been pregnant before why can't it happen again

I've been TTC for 6 months now. I've been pregnant once before when I was 17. And unfortunately wasn't able to keep it. Now I'm 21 and am more than ready and able to decide for myself I want a baby! But it's just not happening for me! My first pregnancy I got pregnant the first time I had sex! So I'm not sure why it's so difficult now! I need some advice or opinions. Could this because of the abortion which I may add was forced.