my pet rat-Sugar

Question
My fiance and I bought Sugar about a year ago from a local pet store in
a small town. Now I notcied they kept their rat pups in the regular
bedding (the dusty kind that can cause respitory infections for the pups)
so her breathing has always been heavy but I hear no clicking when I
listen carefully. I want to know how to help her breath easier. Also she
had a miscarriage yesterday night and I was not aware she had until
morning. When I got to her she had split the babies heads in half n
burried them different places through out the cage. She wasn't with the
male after conception and this was her 4th litter. I just want to know
how to make her comfortable and make sure she is happy. I have of
coarse changed her cage and made it back to normal.  

Answer
Her 4th litter? I suggest she keep away from males from now on.  Next time she may not be so lucky. Your rat should not have so many litters.

Also, is she having trouble with respiratory infections? Is she in a cage or tank?  What bedding do you use for her?  

Why does she end up pregnant so many times?