Hello,
I saw your questions and thought I would respond since I have the very same issue that jade52194 wrote about. I have been on antibiotics a few times this year, 3 times just in the past few months. The foamy saliva with thick gooey mucus gets even more abundant after eating sweets or carbs.
Welcome to the gastroenterology community! Have the doctors done any tests on you? Have you taken antibiotics in the last year?