Why won't my iPhone 4s charge?

Recently, my iPhone 4s has been having problems charging. It started occurring after having used a aftermarket charger (which I have read to be the possible cause of the problem) when my iphone suddenly wouldn't charge.

Here are the symptoms at the moment:

-When plugged in, the iphone doesn't charge, I have to wiggle/bend the charger in order to get it to charge, but as soon as I release it, it stops charging.

-When the phone is dead, the time it takes to charge enough to power on varies greatly: sometimes it powers on instantly, sometimes it takes up to an hour.

-My battery life fluctuates: It will be at 17% then power off, or be at 12% then go down to 1%.

-Obviously because of this I cannot connect to iTunes.

I have tried the following to help fix the problem, but no no avail:

- I have replaced the dock connector, but this has not fixed the problem. (Bear in mind that before the dock connector replacement, the iphone would charge when turned off, but never when turned on. Since I replaced it, the situation has changed)

-I have tried multiple different chargers, wall plugs and sockets. None of them have worked bar my girlfriends one, which surprisingly works perfectly whilst no others do?)

I am yet to replace the battery, but I don't see how just that will fix the whole problem? Help!