Why is the Samsung Galaxy S5 so slow and laggy?!

I got my Samsung Galaxy S5 sometime last year during early 2015 and man is it slow and laggy as hell! I used to have a Samsung Galaxy S3 and I could have all the apps running in the background with no problem, but once I got the S5 and did the same, all hell breaks loose… Just like Windows Vista, I want to throw my S5 onto the ground to let out my anger! >:(

Things I've experienced:
-Let's say I'm on private browsing (incognito) and leave to go to another app and come back to the Internet app, then my private browsing tabs will disappear, leaving just my non-incognito tabs open
-Touchscreen isn't responsive at times
-If you're using an app and then turn off the screen and turn it back on quickly, then my S5 will turn on slightly for less than a second and then turns off again, then you have to wait for a few minutes until it gets back to normal
-The lower half of my phone blinks rapidly
-If I'm writing a email draft and go to another app and come back, my entire email draft will get lost…
-Loading up apps can be extremely slow
-Apps close for no apparent reason at times

So why is the Samsung Galaxy S5 so slow and laggy?!
Is the S5's RAM low or something?
Should I upgrade to the S6 or S7?

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