What kind of bottles are you using? Any carbonation pressure stands the chance of pushing the cork right out of the bottle. You need to secure them in either with a cap or cage. If you're using champagne bottles, you should be able to cap them, but maybe the bell on your capper is the wrong size. If you're using Belgian bottles, check out my sig for a photo thread on capping Belgians. Your corks may be in too far to do that if they're in all the way.
Either way, you probably have some time before there's enough carbonation to push out the cork. My Belgian has been bottled for three weeks and while it's got some carbonation, I still need to use a corkscrew to pull the corks out of mine.
I see you're in DC. Check out Meridian Pint in Columbia Heights. They have a Bombers for Brewers Program where they save Belgian beer bottles. They're not cleaned and are nasty and need to be thoroughly cleaned. I got about 40 from them and gave them a few days in an Oxyclean to loosen the residue and remove labels. Then SEVERAL hot rinses and scrubs with a bottle brush to get them all clean.
