maybe invest in some proper lycra padded shorts and some udder creme.
riding 7-8 miles on a commute isn't the best preparation, try increasing the distance over time. it doesn't take long before 50 miles is done in a few hours and it doesn't even knacker you out st the moment you are looking to do a distance 14 times longer than you are used to. if you can do 50 with no bother it's only 3x longer.

in short HTFU