So I'm lv.19 (new, I know) and when I was a much lower level, I was getting a decent amount of treasure chests which I figured was decent money for a low level. Now, my friends are getting those treasure chest drops fairly often and they tend to be higher levels than me but I've only gotten one in... a long time, I was wondering what factors affected drops?

You probably got the "Brown Chest" It is a chest that only can be opened by the key that you buy from Token Shop. The Key you looking for looks like an purple egg, in the 1st tab and 2nd page of T - Shop for 8 T points.

The chest will drop one of those.

lv30 Armor ticket (7,15,30 days)
lv30 weapon ticket (7,15,30 days)
Con pot ( gives +15% CON for 10 mins)
Sol Pot (^)
Eng pot (^)
STR pot (^)
S (Small / 100.000) Autopot for LifePoints or Energy Points