So I'm nearing "drinking day" on my first home brew. It was a simple amber ale extract kit from Midwest. All went well as far as I can see, save for one thing. Today is day 11 in bottle conditioning. I cracked one thinking it'd be nearly finished but instead I find a beer that's still pretty flat. Very tasty, but no head on the pour and a flat taste. It did make a little "tsst" when i cracked it. I understood the bottle conditioning and carbonation phase should be 2 weeks. Surely 3 more days won't do much good. What could have gone wrong?