This type of soreness is because your butt tissues are compressed and thus oxygen deprived. They'll get used to it. The usual prescription is to ride only 1/2 hour and try to do that every day. If soreness becomes a problem, give it a rest day or two, but keep at it. It'll probably take a month before you can ride much distance without soreness afterwards. I'm not sure how much padded shorts help with this as they increase the area affected. Same with padded saddles - they make it worse if one sinks in at all. Stiff padding that doesn't feel like it compresses is good. I've been off the bike for 2 months, doing other things, and I'm going through that now. I'm going to run today, ride again tomorrow.