I have a glitch with my iPhone 5c?

In April, I got my iPhone 5c as an upgrade from my 4, which was slowly breaking since I had it for two years. It was going great until I dropped it in the beginning of June. Luckily enough, there was an iphone repair store around the corner from me and they replaced my screen glass. I heard from a friend who also had a problem with the 5c that they did good work for reasonable pricing. After I picked my phone up after fixing, I noticed it was a bit heavier but didn't pay much attention to it because everything was fine. A few weeks ago I noticed screen glitches becoming more common. When I first unlock the phone, then use it for a few mins, the texts looks disorted, almost as if it's running down the phone because it looks like little lines. After I'm on it for a good minute, it blinks and lights up and it's back to normal. It happens half of the time after locking it and reusing it. I also noticed that the top banner has recently showing up when I click a picture on Facebook and is transparent through the top of the screen next to the "Done" button (those who use facebook know what I mean by that). I just noticed it was the same way in Instagram. Does anyone know what is causing this and what may a possible solution? It's not effecting my usage, but it's annoying and I hope it won't cause a shut down all together.

PS: the phone may still be under warranty from the place I fixed the screen, I just want to be able to know what I'm talking about if I have to go in again.