Karen Marie Moning. I love her and have read both of her series. The first one is called The Fever Series. The second is Highlander. They intertwine together so in the middle of The Fever Series, you should start reading the Highlander because the characters will have story lines together.
Here is her Goodreads Link https://www.goodreads.com/author/show/4 ... earch=true
And here is her website
http://karenmoning.com/