If you do a search you will find an incredible number of threads on this an related topics. It's all about saddle time, quality of shorts (to a point), saddle and saddle adjustment. Too much padding is a bad thing. Chamois cream can be a good thing. The padded saddle that feels great for 10 miles might be a nightmare for 40 miles.

I'm not familiar with Baggys, but does this sort of short have an inner sort that keeps the padding from sliding around? Also, are you saying you were ok after the first ride, but very sore after the second? I associate baggy shorts with mountain bikers who seem to spend a lot of time out of the saddle. For road bikes lycra shorts are really preferred for longer rides.

Do you get out of the saddle occassionally (stand and stretch) or pedal standing? My rear can get painful after about 2.5 hours, but yesterday we had to walk 1/2 mile up a very steep stretch well into a 70 mile ride. I was in rear pain prior to that, but felt fine after walking for a few minutes. Says something for blood flow and air flow.