I took prenatal yoga at Ohm Baby with Holly. It was great. She starts class with a discussion of a certain birth or babycare topic and then gives great poses and exercises designed to assist in labor and relief is pregnancy related pain. I really liked it. She also does baby and mommy and toddler and mommy yoga but since I work I can't attend. She also has nice workshops. They have a website if you do a search and are located on Market Street in Camp Hill. I would recomend it.
Re: prenatal exercise classes in Mechanicsburg area?
https://classes.strollerstrides.net/hershey/location/index.aspx
Note sure how far it is for you to get to Hershey...but I think she may also have classes in Harrsiburg.