Preterm labor

I went into preterm labor at 28 weeks an they got it stopped. I'm still having contractions off and on but not dilating so that's good! Now I'm almost 30 weeks and my dr. Is worried that my cervixs is shorter already I have to get an ultrasound done to get the measurement of it. I'm also not gaining weight from my last appointment. Anybody else have this happen, what was the outcome, how far a long did you make it? I'm so worried he's going to come to early. Thanks in advance for the advice!