Hi glossyflower,
Congratulations on your pregnancy! Glad it has come as a good surprise.
I'm 14 weeks now with my first baby and I can totally empathize with all the horrid symptoms you are having and I imagine the time is really dragging! I'm feeling quite a bit better now so I know everyone says it, but you should find too that in another 6 weeks you'll be feeling much stronger- especially once you've had the scan, which really brings it home how worth it it all is! :)
When we found out we were pregnant, we felt like all the books were telling us we really should wait till 12 weeks before telling anyone, but it just wasn't possible for us and we had to tell family members, for quite a random reason... my boyfriends's mum had booked a spa day for me, her and boyfriend's sister the following week as a birthday treat and had me booked in for a massage the following I phoned the spa and they said I could no longer have the massage due to the pregnancy and had to change it to a pedicure. I knew there was no way the boyfriend's mum wouldn't cotton on to my treatment change when we got there so we had to come clean at just 5 weeks pregnant! And of course it wasn't fair for his family to know and not mine, so we told mine as well!
I came clean at work too as I wanted them to be understanding about me struggling and having to work from home some days when I was particularly exhausted. It sounds to me like this would help you hugely if you could tell your work, and I would go for it. You need to do as much as you can to reduce your stress levels and having the understanding of your colleagues will mean a lot.
We were worried about the scan going badly, as is everyone I guess, but to be honest by that point we both couldn't have given a stuff who knew and who didn't, all we cared about was our baby. If anything had've been wrong, as you say, people would have been understanding and I'm sure they would have given us our space. As it was, the baby was in there doing fine!
About your wedding dress... I can't say for sure it will be the same for you, but I had massive bloating early on as well and it did actually stay about the same level for ages, rather than getting any bigger- I only got even bigger again at about 12 weeks. I was eating like a pig and doing no exercise as well, so I reckon if you eat sensibly and do a bit of exercise over the next couple of weeks to be on the safe side, your dress should definitely fit fine.
Hope this all helps! My instinct would be to tell people anyway, make your life a bit easier. x