One pill makes you larger and one pill makes you small. And the ones that mother gives you don't do anything at all.

Ok. Here 's the meaning. They are the same girl. My idea is that the girl is trying to save herself. The upper glass means now and the future, and lower one is the past. Water is time. She feels trapped in the time and it goes so quickly that everything she's trying to keep is going away. She misses her past(who is in the lower glass and will never be able to come up again). Those things on the upper glass are what she will encounter in her life. And when time goes by, they entered into the lower glass, becoming "the past". The pearl is what she loves and wants to charish, but it will become the past anyway. When those things enter the lower glass, most of them sink to the bottom of the glass which means she forgot them. Only a few float on the water that she will remember forever.