I agree with the others - it's your news to tell when you're ready! I have been feeling that folks around me might suspect too, so to head off the questions I have been dropping "gosh I need to lose weight" in the conversation every once in a while, so that they might think I was just eating too much and feeling self-conscious. That will usually keep people from asking!

For example, out to eat with my mother-in-law a few weeks ago I made sure to say "No wonder I can't lose weight, I have no self control!" when I had an empty plate.

It also works for me when people offer me alcohol - "No thanks, I really have to lose weight. I am trying so hard to watch my calories."
Just be careful not to talk about any of the give-away symptoms, like nausea, stuffy nose, aching breasts, etc.