Oooops!

Hmmmmmmm, something happened last week while we were on vacation that is causing me to worry....
Sunday night, while we were baby-free, Rob and I partook in some "alone time". As an aside, it was MUCH needed! Anyway, the responsible smart girl that I am remembered to pack lots of condoms. The idiot scatterbrain that I am forgot to use them. I didn't think this was a big deal at the time, thinking my period was due this week. Then when we got home I happened to glance at my bedside calendar (every month I have the best intentions of actually charting, but instead just mark when my period starts) and I realized (with a sinking feeling) that we did the dead on cycle day 14!!! Um, big deal since I usually ovulate around day 14 to 16! UGH!
So here I sit, a week away from being able to test, stressing out over whether or not I might be pregnant!
Now I realize what a blessing it would be (since I only have one ovary, scar tissue, etc), but the timing couldn't be worse! I would be 16 weeks pregnant at the wedding and there is no way that my dress can accommodate a 16 week belly (esp. with a second baby).
Okay, let's look at this rationally:
1. There is only a 20-25% chance of getting pregnant on any given month
2. I don't feel pregnant (but then again I never did with Ryan either)
3. I can't possibly get pregnant the one time in a MONTH that we actually have sex, can I?
DEEP BREATH
I figure Friday is the earliest I can test, but I am really chomping at the bit to test now...
On the plus side, I started having some cramps today and since giving birth I have been getting crampy around mid cycle and they last until my period starts. Not to open up a whole other can of worms, but anyone else get this? Should I worried? When is the earliest I should test?