Why are my guinea pigs stinking up my room?

i have two female piggys. i got them 3 months ago when they were just over a month old. and for the past week they have been making my room smell like pee. i have them in a c&c cage. and its not like i just have fleece. i have 2 layers of newspaper, three layers of towel and then two layers of fleece. plus i change ALL of that every saturday. but for the last week they have been smelling so bad. i really dont know why. its not like the pee is just sitting there. it should at least get some form of absorption. right? so yea... uh thx for our replies!