iPhone not turning on or being detected by itunes after screen replace

I replaced my screen and everything turned on and worked perfectly for about a week and a half and then my iPhone 6 plus started acting funny (locking up, being slow to respond) then one morning I woke up and it would not turn on at all and was not being detected by iTunes. I replaced the charging port because the original looked burnt on the inside but it didn't seem to make a difference. I would really appreciate any suggestions on what was wrong as I cant afford a new iPhone at the moment. Thanks!.