Hey Jojobananas. You and I share the same starting stats...including height. Anyways, I hear you on being discouraged...it's a grueling diet and it definitely takes a toll especially when the scale stops moving. However, I don't think what is happening is abnormal or cause for concern and here is why.
1. First week you had a huge loss!!!! Way to go!!!!!! I lost 7lbs my first week and only 1.2 at my second weigh in. Furthermore, whenever I went in for weigh-ins (which was Friday morning) I would notice the scale tip down a lb or two on Sunday usually.
2. Like others have said, it would be great to loose that much weight every week but its unlikely. However, even if you loose only 1 lb this week you are still averaging 9lbs in two weeks which is incredible. Some people (and bless their hearts because I would have been sooo disappointed) only loose very little their first week.
I did IP phase 1 for about a month and a half October 2012-mid November 2012 and lost nearly 30lbs. I am doing a reboot to loose 5lbs and hopefully finally get to 130.
IP works...but its not without some mental anguish. To try and buffer that, take a day or two break from the scale, focus on all the healthy foods you are feeding your body, watch a funny movie, get on here and write, take a bath, or do anything that will make you feel good.
I felt as you are feeling now many times and felt like giving up at points too. However, you are getting closer to goal and when you arrive, you will not only weigh less but you will have a mental strength and stamina that you didn't before. You can do this. We are all here cheering you on!