Bmac - You are the same person you were before you drank. So now that you are sober, you're facing those same existential questions as before. Drinking did not solve them... just covered them up.
Joy in one's life. What we all seek and it is highly personal. Finding meaning did it for me. When I was drinking, I couldn't care less about anything. Someone asked me my philosophy at that time and I just said I am just taking up space and waiting to die.
How to find meaning? Again... highly personal. Religion? Philosophy? Family? Work? I dunno what works for you. I hope you find it tho. Feeling you just exist is miserable.