Robitussin DM?

hey ladies, 30 weeks & been having a cough for a solid week & it’s getting worse each day. Went to my ob yesterday and he said to take robitussin plain, brought the Robitussin DM. Not sure what the difference was but I did lot of research and it’s expected to be okay plus it’s alcohol free. Took a does last night and one just now before work, I’m super nervous though because I hate using medication unless it’s my last option. Has anyone tried it? What’s your opinion?