How soon does a belly show?

I stopped using BC recently. as we will be TTC soon. We are getting married in 4 months, and were going to start trying for a baby as soon as the honeymoon. the plan was to use condoms until then, but old habits die hard and we went unwrapped. I think I may be pregnant a little earlier than planned. this is not a bad thing, as I said we were going to be trying soon anyway. My only actual concern is my wedding dress. if I am pregnant, will a belly be showing in 4 months? my dress is quite tight in the torso and I really dont want to show a bump on my wedding day.