iphone 4 not charging

for the last few days my iphone 4 will not charge when i plug my charge in. I thought it was bad connection or my charger was not working well. I tried other phones on my two charges. The chargers work but for some reason i had to fiddle with the charger when connecting to my charger my phone. I figured there might be issue with my port. I tried removing lint form the port and still it will not charge. I tried restarting my phone and when i turn off my phone then plug it in it starts the phone up. I tried charging the phone when the phone was off and surprisingly the battery life percentage has increased. but there is something seriously wrong. the only thing i haven’t tried is syncing my phone to my pc