Why do I suck at golf so much?

I've been playing since i've been young and now i'm a teenager. I can't break 90, even though i've played 8 rounds already this summer. Today I played 9 holes and I constantly duffed my irons. I use a 3 wood off the tee, but today I tryed my driver because I didn't give a sh** about the round anymore and I had the biggest slice. I concentrated on following though good and stuff too. Help!