I assume you are looking for a liquid cold medicine - there are some that are sugar free, for dibetics. You could also try a table form. There are also sugar free throat lozenges.
I am a strong believer in Cold-eez, especially if you start taking them in the first 24 hrs of your cold - but the SF can be hard to find. There are also homeopathic remedies, like Occicillinum (sp?) that have no sugar, but I have not tried them.
I would be careful about side effects - I have noticed that effects seem to be exaggerated - I took a decongestant pill the other day for a sinus headache, and felt like I had had too much to drink! - Would not have been so bad, if I hadn't been at work and had several important meetings!
You could also try my grandmother's remedy - lots of Vick's rub on the chest, a hot toddy (rats, no whisky allowed - oh well, hot tea),then go to bed and pile on the blankets.
Good luck, hope you feel better soon!