House Breaking A Dog...?

Okay so we just got a new english mastiff puppy. She is 11 1/2 weeks old. We are trying to house break her but aint haveing much luck so far. We have a cage that shes in all night she eats 3 times a day morning lunch and supper then she is put in the cage and 15min or so later we take her outside. She goes sometimes. Normally she just runs around and plays then when we let her back in she goes and finds a place on the floor. I've also tryed saying NO! or clapping my hands and whistleing at her when I catch her but she just keeps going. She knows she has done something wrong because after she does it and you say come here she whimpers away. Its becomming very frustrating and we are thinking of taking her to the SPCA. Any tips would be a big help. Thanks in advance!