What Is The Cause And Treatment For Recurring Dandruff?

hi, i was wondering why i get dandruff, i have never suffered from it and suddenly in december my scalp started getting itchy and now i just keep getting dandruff. when i use t/gel it seems to work but not 100% but i dont want to use that forever so i was wondering if i use it till the bottle is done and it works will my scalp go back to normal and will i be able to start using whatever shampoo i want on my hair again or does this mean im going to suffer from this forever? also im on 75mg a day of venlafaxine and it seemed to have made the skin on my face break out so would it cause dandruff? thanx