My puppy can't seem to house train!?

My 3 mth old puppy is completely crate trained. I feed her twice daily. In the morning and evening. I take her out about 5 minutes after she eats and drinks. Then again about every 15 to 20 minutes for the next hour after she eats. Then I make her wait longer, about every 30 to 45 minutes unless I see her sniffing around. I praise her when she goes outside. She is quick when she does it in the house, I never seem to catch her in the act. I keep her in one room of the house and do not let her roam. She is still pottying in the house, about 5 times a day! What am I doing wrong?