Q: my phone will not keep a charge or won't let me charge it

Take it to Apple for evaluation, most likely you have a defective battery or board.    

If Apple determined the device is fine, that only leaves the charger.

Ive got a funny feeling I'm about to be told the same thing... although I've tried 3 apple chargers and 2 aftermarket ones and still nothing.

This happened to me last night. Unforunately I had to get my phone replaced.

Things to check for first:
- wires in the cord are not managed at either end

- blow the input to get any lint/dust out or use an air compressor to be sure about it

- check the charing input for any light yellow discolouration = moisture damage

if you have checked these main things and they did not help, you should go into your closest apple store!