is this your first 30 mile ride? did you go a bit slower than usual to get the longer miles in?

If so, your arse is not used to that much time in the saddle. I would just do a few more of the same time rides as this one and remember to get out of the saddle more during the ride stand up for 30 seconds every 10-15 minutes.

If your still tender after a few rides of the same time then onward the for a saddle searching you should go.