Galaxy S5 plus problem!!

I have purchased a galaxy s5 plus 3months ago. And for a week now, it started doing this weird thing! Almost everytime I try to unlock the phone, the screen flickers a yellowish tint. Sometimes it takes 2 or three tries to get the device to display correctly. there are times when it flickers and goes blank, then I'd have to lock and try again a couple of times, and other times it just flickers and displays correctly right after. The problem never occurs while using the device, only on unlocking.
I wonder what the cause might be. And if anybody had a similar experience and has a fix, please help!
My galaxy s5 plus (sm-g901f) runs on android lolipop 5.0.2.