Why can't I get pregnant??

Hi, I am 19 and I cant seem to gat pregnant. I've been pregnant before but I got an abortion and I never went back to the doctor because I felt fine. Now me and my boyfriend are trying to conceive but we've been un-successful...why is this? I had my period last month but lately I've been waking up nauseated with no vomitting, and I've had alot of watery discharge....Help!! !