I've been spitting out clear phlegm with a lot of bubbles in it for about 3 or 4 months now. is this normal? what could this be?

Reflux: Bubbly, clear phlegm at your age, w/o other signs or symptoms, suggests (to me) reflux of saliva from the esophagus or stomach. Average human makes about 1 liter (bit less than 1/2 gallon) of saliva (spit) per day. Most of that is swallowed & recirculated after absorption. For people with problems with reflux (or, rarely, something obstructing esophagus or shrinking size of stomach), it comes back