Something keeps draining my 1998 Oldsmobile Intrigue

I recently bought a 1998 Oldmobile Intrigue and it
was running great until one day the battery was
dead when I went to start it, so I jumped it and it
started right up and didnt do it again for awhile, but
then it started going dead more frequently. So I
replaced the battery n it still went dead, i then
replaced the starter which you could clearly see
was a brand new one n the battery was drained
completely in only the matter of time it took to
replace the starter an the battery was
disconnected the whole time. So I changed the
alternator which you could see it too was brand
new an it still won't hold a charge an the only way
to get it to start is to leave it sit on a battery
charger or 8 hours or longer. Whatever is draining
the power to my car is strong enough to eat up a
new battery, new starter, an new alternator. The
person I bought my car from must of been having
the same troubles with the car as I am now but
failed to tell me about it. And I don't know what
else to do or try and I also don't have alot of money  
to keep putting into this car.