After what seems like an embarrassingly short 9 miles worth of errands today (the first of which was to get a new lock for my new wheels) I am a little sore (my ass more than anything) but overall I feel great. I dig my new mode of transport.
Haha! Thats what every new-in-anything has do endure - the pain of the bleeding noob.
It will vanish after a few rides. If not, you should ask someone on your saddle (softer is not necessarily better btw). You should literally sit on your bones. Try to ride every day, it does not need to be for long. Even 2 miles are ok to get used to it.
But you have none of the protective thingys? (mudguard??)
I wonder if you can put a bicycle basket on that back? I like it not only for shopping (dont forget a cotton bag, folded on goes on every pocket), but also for putting books in when going to the library.