Can you really just say that you've stopped drinking and decided to keep it that way because you feel much better without alcohol? Your antibiotics excuse might fit into this perfectly - you did not drink while on them and now don't want to. Being polite and making no more lies - who can argue with someone wanting to improve their well-being? I would not tell coworkers and a boss that I am an alcoholic, though, after getting sober. Just say you don't drink, period. You do not owe colleagues explanations to your lifestyle choices. This way you only need to say it once and then no additional talk necessary.
Enjoy the sushi - I love it too!
