When people say, "do whatever makes you happy..." they really mean, "do whatever gives you joy." But there's more to happiness than that.
It's possible to experience a lot of joy... but be miserably unhappy.
Some people enjoy getting stoned... but they're not proud of being drug-addled. And while they're enjoying new highs, their happiness is at new lows.
Some people achieve amazing sports feats... by cheating to get there. It may be fun, but does it generate happiness?
To be happy, you need to have an identity in your life, and that identity derives from your purpose in life.
If you have a purpose in life, getting closer to it will make you happy.
If you have a purpose in life, your life is meaningful - it's about striving to fulfill that purpose.
Lastly, check out my friend Claudio Etauri's site.
He has multiple sclerosis, and how.tobehappy.org/iwalk is his effort to raise money for "liberation treatment," a revolutionary treatment that has helped some MS patients recover the ability to walk, from either great weakness (e.g. inability to lift a foot over a door mat 2 inches high) or even from a wheelchair!