What is wrong with my pregnant guppy? 10 POINTS?

My pregnant guppy is staying away from the other guppies, not swimming as much, not eating as much, & is losing her tail. I thought that the male guppies were nipping at her tail but when i put a divider in the tank to separate her she is still losing her tail. This is my first time ever having a pregnant guppy so I'm not sure what is normal and what is not.. please help me!! 10 POINTS FOR BEST ANSWER!! PLEASE I DON'T WANT HER TO GET SICK!!!