burning oil

ok my car just rolled over to 90K, and lately shes been burning oil like a crazy crack whore. Anyway... like i just got the oil changed in it, and this past week, i have added a whole other quart of oil.
The oil is already dark brown/black.. and its barely been 1000miles.
Shes consistantly low on oil.. i dont have any leaks... i dont get it... is that just normal since shes getting old?!