Pre term labor question help please

Three weeks ago I had to spend four days in the hospital stopping preterm labor first they put me on magnesium and then as soon as they shut the magnesium drip off in my IV my contractions came back two minutes apart they finally found the mix of magnesium and Procardia to make labor stop completely since then I've been on 20 mg of Procardia two times a day every six hours and on bedrest I almost feel like the pills aren't working as well anymore since I've been feeling more contractions... Any input ladies