I can't add much to what the folks above have already said - other than to say DON"T GIVE UP.
You will have bad days and good ones... Sometimes you'll feel like you've won the Tour de France; other times you'll feel like a complete idiot. The learning curve can be steep (though you've come to the right place for excellent and practical advice) and you will experience pain and heartache. Just don't give up.
If commuting by bicycle were easy, everyone would be doing it. As it is, you've chosen to be one of the few. In a few weeks you'll have some hard-won experience, better fitness - and some great stories to share. We'll be here to listen.
Oh, one more thing: Don't give up.