Backlight problems following screen replacement in the end of April.

Okay so this past week or so the backlight would suddenly just stop working and I'd reboot the phone multiple times until it did work, and eventually each time (around once daily, twice a couple times) the screens backlight would return. Now, I didn't know this was the issue until today, when I went and got a new phone and noticed that when a light shined directly in I could see things on the screen. I'd like to know if this happened due to overheating or if I had a genuinely bad repair or if there's something I can easily fix without breaking anything (I work on computers but phones kinda scare me since everything is so teensy).