What do you take that is safe and works for a cough?

I have been taking the Robitussin DM my doctor said I could take but it doesn't work all that great. I am now on my second course of antibiotics because twice it has gotten so bad that I was coughing up infectious looking stuff. I think it may be bronchitis because I have had it for over a month but there isnt' really much they can let you take. I am 20 weeks and am just wondering if there is anything else anyone knows of that I could ask my doctor about. Thanks