Preterm labor and Dilated at 28 weeks. Help!

I've gone into prelabor 3 times now, 23 weeks 2 days, 26 weeks and 28 weeks 4 days. Positive fFn test at 24 weeks. At 28 weeks 4 days when I went into labor, they told me I was 1.5 cm dilated and 50% effaced and she could feel the baby's head. Sent me home once contractions completely stopped with 2 doses of terbutaline. The last 2 times it's only taken 1 dose. How long should I expect to carry now with my cervix changing? I am on Procardia every 4 hours but still having contractions, just not regular or close together.