the problem is the back tire just started rubbing against the frame. this literally happened 30 min ago. please help me fix it!!
I'm going to guess that the wheel slipped in the dropouts (where the wheel's axle enters the frame).
Loosen the nuts that hold the wheel's axle in the frame. Push the wheel back into the dropouts all the way (depending on the frame, you might not do all the way; the wheel should be sufficiently in the dropouts). Check that the wheel is centered. Then, tighten the nuts.