My Rat is or was pregnant!

Question
OK so bought a female rat from my local pet store and about last week she got fat I mean really fat. and she started acting really strange the other day well when i got home from work today shes not fat was like she was when I first got her so my question is was she pregnant , If so where are the pups I looked everywhere in the tank did she eat them since this could be her first litter. I also put her by herself yesterday so I'm a little confused could you help thanks. OH is it possible for first time mothers to abort the first litter

Answer
Did you dig in the litter for the pups?

Also, if the mother rat is unable to lactate, she will eat the pups leaving little or no trace of them.  If they were stillborn she would also dispose of their remains.  You said you put her by herself  yesterday .....what do you mean by that?