Can drinks that are caffeine free still keep you up at night?

So I got into a habit of drinking some caffeine free ginger ale or pepsi with my meds I take at bedtime. It seems I have a hard time falling asleep and do not get a good nights sleep. I know there is sugar in soda, but when I was younger I used to drink Mountain Dew at night, during the night and it was fine; My Dr told me not to have caffeine after 2 put these sodas are caffeine free?? What gives????