Crashing apps and problems unlocking

I am experiencing problems with some apps: facebook, skype, mydol and some others keep crashing while using them, switching to them from other apps or just when I unlock my phone. I’ve had this problem for a while already and have tried doing a hard reset, after which everything worked just fine for a while but the problems came back. Now accompanied by no reaction from my phone when I try to unlock it (pressing the button to show the lock screen: the screen stays black). Sometimes the screen will turn on after a couple of tries, but sometimes I have to turn off the phone for it to restart completely.
(I have also had the bloated battery issue and fairphone has send me a new one, but I don’t think that has to do with these issues)