J.O.
At about two months, I felt like my pants didn't fit right anymore. It's not that I couldn't get into them- they just felt really uncomfortable. I started wearing dresses at that point (usually pretty form-fitting ones) and started getting comments from co-workers right away about me already showing.
I did get really big (by the end of the eighth month I was bigger than I should have been at full-term) BUT - and here is the big BUT- it is because I let all restraint go and ate a TON especially for emotional reasons.
So even though you're showing early, it doesn't mean you're going to be huge as a house later on- just don't do what I did. When you're "eating for two" remember that one of you is really really little :) If you follow a healthy eating plan and stick with a safe exercise routine, you (hopefully) won't become a beached whale like I did.