Hello and welcome!
Good luck, I've just survived the first week and wouldn't have done it without this site! Read as many of other people's posts as you can and you'll find that everyone else is going or has been through exactly the same as you're going through today and will experience over the next few days. There's bound to be someone else starting today who you can share experiences with.
Personally, I'm on cloud 9! I wish that I could bottle how I feel today, all the tiredness and crap has passed, I don't feel in the slightest bit hungry and have loads of energy and enthusiasm. Next week you'll feel exactly the same and you'll be well on the way (weigh!) to target x