I was recommended to get a night guard not just for grinding, but because i had the lower left rear molar extracted and will not be getting an implant. should i get an upper or lower guard?

Depends: If there's a tooth behind the empty space where that extracted molar was it most likely will tip into the empty space. So I would recommend replacing that tooth as early as possible and get a lower night guard for the mean time it will double as a retainer.

Consult your Dentist: Jennifer, This would be best answered by your current dentist. There are many designs & material options that can be used when making an oral appliance whether it be a night guard, retainer, orthodontic appliance, etc.... Each dentists may have his/her own preference but that does not mean one is better than another. Go with your dentists recommendation. Good Luck!