i saw a ufo

i was working late with my dad one night fixing the trailer out in the country in Illinois US and it was about 2 years ago in 2010 late in the year in the fall. i stepped aside to go pee behind the shop and when i looked up i saw a rapidly bright flashing ball flying through the sky moving as fast as lightning. it flashed about 3 times before it flew all the way across the sky so fast i did not have enough time to go into detail but each flash was about each second long and faded out. i ran to tell my dad but he did not see it so i was very disapointed but after that about 5 minutes later i went back behind the shop to look again and i saw a light from a helicopter flying across the sky. maybe the driver of the helicopter saw it too. i know i saw a ufo and it was way too fast to be a fake or a jet. does anyone have an explanation?