What Causes Gum Infection?

My gums and top teeth have been feeling slimy, like they are covered with some layer of thick but extremely slick goop. Has been going on for a few months, out of nowhere. I have tried absolutely everything, baking soda, high quality mouthwashes, electric toothbrush, tongue brush, cleaners, scalers, drinking tons of water, NOTHING works. The only changes I made in a relevant timeframe prior to this occuring were quitting smoking, and I also significantly lowered my milk consumption. But the slime feeling didn't start until some time after both of those. I have been exercising a ton since about the time this began if that matters. It's driving me crazy, I brush and brush and brush, scale, floss etc and every day like clockwork the slimy feeling perists.