go get it x-rayed, seriously.
I had a friend that had the smallest piece of glass stuck inside of his foot and he left it there for 6 months.
After 1/2 a year it started to swell slowly, and over a month time his foot doubled in size due to the swelling and becoming very painful.
If you are about 80% sure that there might be a BB in there its worth the effort to go get an xray.
save yourself some pain incase it does eventually get infected if there is something lodged in your hand