So I ride a '78 Raleigh I inherited from my parents. It seems to be about the right size for me but I haven't really had it fitted in a shop. About two weeks ago I started commuting home from work about 5 nights a week, about 8.5 mi a night. About this time my butt started being really sore every ride, almost right away. I've messed with the seat height and tilt a couple times and can't figure out if that's actually the problem. It's starting to become very frustrating so I was wondering if anyone could help me diagnose the problem. I also thought it could just be that I've just started riding this regularly, before it was only about 15-20 mi a week for a couple months.