Answer:
did you try taking the backing off and seeing if it's an internal problem
Step-by-step explanation:
because if so then that could be the problem. Of course i'm not saying take your whole phone apart but if you have any family that knows anything about phones or how to help inspect it then that might help you in finding the problem. Unfortunately i do not know to fix the actual problem I can just give you advice on what you could do to find the problem.
I'm sorry that I can't give you any tips on how to fix the actual problem but i can give you that little tip to find the source. If you do this tho check under the battery and then check where the plugs go.