Chihuahua mix, restroom problem

Question
I have had my Chihuahua now for about 4 weeks.  We bought her from a lady in our Winn Dixy parking lot. She is 6 months old.  The first 2 weeks she would use the restroom everytime we took her out, which was about every 2 to 3 hours or when we saw her sniffing around.  Then for some reason, she will not go poo outside.  She also pees in the house every chance she gets. When we take her outside, sometimes she will go but sometimes she will hold it until she gets back into the house. We have to watch her constantly or she will go in the house.  We thought she was housebroken for those first 2 weeks, but now we don't know what made her change. We have 6 acres of land and mot of it is wooded, but we have much lawn around our house.  so she has plenty of places to go. We have had alot of rain, but there are plenty of times that it was not raining and she would still go in the house.

Answer
most dogs pee to mark their territory -- that might be whats going on. not going poo is a problem. you could call avet or ask one on here. take her out and if she dosen't go, leave her in the yard and watch her until she goes. if not, i would get some indoor mats for her. hope this helps and feel free to follow up =]