The Unloved Ones Series by Kevin Richey

Unpretty
What if you could become thin overnight?
Katherine Blythe is an overweight teenager who, on her sixteenth birthday, wishes to be thin, only to find her wish coming true with alarming side effects. As she loses over half her weight in the span of a week, she finds the world is a different place when you look the way you’re told you should.
But is her wish responsible for all this? Or is there something else going on—something distinctly supernatural?

Uninvited
What if you could become the girl he left you for?
After her boyfriend dumps her, perfectionist and overachiever Jacqueline White obsessively compares herself to his new girlfriend, the sloppy and irresponsible Becka.
But when she wakes up in Becka's body to find they have switched places, she has a choice to make—should she take this opportunity to destroy her opponent's life from the inside-out? Or should she instead find a way to keep this new body, and her old boyfriend, for herself?
Find out in this dark homage to Freaky Friday.