i didnt think any of the over-the-counter ones were safe if they contain decongestant. When i had a cold when pregnant with ds i inhaled menthyl crystals (only use one crystal in a bowl of hot water as they are strong).
if you have a cough, i would either take glycerine or see your doctor.
I've had a terrble cough too and thought I was going to cough this baby out! I got a Glycerine & Lemon cough mixture from Sainsburys - doesn't really do anything but coat your throat a bit. The thing that helped me most was Fisherman's Friends (recommended by my GP). They taste absolutely disgusting, but they stopped me coughing.
I had a virus in early pregnancy which affected my chest and throat and the doctor prescribed codeine linctus but only one spoon before bed allowed so was pretty pointless. I just sucked on honey & lemon lozenges to keep my throat getting too dry