What is the best way to help gums infected with gum disease? I have sore gums, especially in the back of my mouth, but I do floss and brush daily. Is there anything I could be eating or drinking that makes this worse? .

Bacteria control. Bacteria grow in the valley around your gums. Brushing reaches 1mm and floss removed 15% of the plaque. You need something like the perio protect method that has been shown to be a better treatment than deep cleaning j clin dent 2012) and it also has been shown to kill 99.98% o the bacteria that cause the disease j den res 2007. Used daily the bacteria do not grow back. Look up perio protect.
Sore . Sore or bleeding gums are signs of gum disease. Alcoholic or acidic (sodas, sports drinks, etc) drinks can have a negative effect on your teeth and gums. However, these alone will not cause sore gums. Seeing a dentist or periodontist for a periodontal screening would be the best way to start.
It's . It's probably not your diet and as stated above the sooner you seek professional help the better off your gums will be.
While . While diet can have a minor influence on gum disease, the best approach is to be seen by a dentist or periodontist for therapy and maintenance, usually every 3-4 months.