Freaking out about cough medicine

[blueberry23]

16 weeks pregnant and after nights and nights of coughing I googled whether the Robitussin dry cough med was safe during pregnancy - my Google search seemed to say it was ok but to be safe I took a half measure, just 5ml.

Asked a pharmacist today and they said no, not safe and shouldn't be taken during pregnancy, they said no cough medicine was safe other than stuff you can buy for kids of the shelf,

Freaking out, hugely anxious - can anyone reassure me?

One dose isn't going to do anything so I wouldn't be freaking out.

What're the active ingredients?

www.drugs.com/pregnancy/dextromethorphan.html

I can't see one half dose doing baby any harm, I think its more if you take it for a few days, multiple times a day like for a really bad cough.