You say you are an "Uber-Clyde" I wonder if the backpack is to tight? Personally I cannot stand wearing a backpack for any length of time on a bike. A rear rack is cheap, try strapping it on there, if that helps, get panniers. ( or a milk crate and go properly "fred" ) The other thing is, time of day. Some people just don't function well early. Did you try your weekend ride at the same time?