problems with iPhone 5c

This could be caused by one of several things.

-You have have dropped the phone recently, or immediately before the issue, which caused damage to the LCD.

-You may have water damage in the phone causing this.

-The most likely cause of this issue though is that you've had the screen replaced before from a third party repair shop and it's a faulty screen. I would suggest that you go back to the same shop and see if they can do a warranty repair for you.