Do you have a parasitic drain? A drain from something in the vehicel when the engine is off. I would either get an AMP clamp or take it to a shop and test how many amps are drawing from a known good battery with the car off. You should nearly no amps on the ground wire.
Do the lights turn on in the dash? IF no then you have a drain, or you have a bad battery. If yes, then you have a bad starter or corroded cables and there is no flow. You could also take your battery to an auto parts store and ask them to test it. They should have a tester in the store that will test batteries.