When did your belly show with the first baby ?

I’m currently 21+4 and I have no belly at the moment, however I have a wedding in 6 weeks and just wondering if anything will change by then. I have a really nice dress which I only wore once and I’d really love to wear it.

Also how do you ladies shop for events in advance?

Like do I just go up 1 or 2 sizes than what I’m currently wearing?