Car stereo speakers only work half the time?

i have and 07 chevy classic and ive been having trouble with my stereo speakers, the front left driver side speaker is the only one working all the time, all the other time the right front side and both the back speaker do not work, but on certain days they will,the right front will work and the back 2 will still not work,and then one day they all will work and the next day its back to just the foint left working, i dont know if its the wiring or what, im just looking for some answers and what i need to do to fix it. also the speaker are not blown being as how they work every now and again, but on the right front if i change my audio just to that soeaker i can hear the music coming out of the speaker but very faintly,but ive checked it and it is not blown. but any help would be appreciated.