What did I do wrong?

Things have been going great for the past two weeks.  I met my goal both weeks, I didn't cheat, I kept working out and I stayed motivated.  So what happened?  Why have I not only not lost but actually gained weight this week?  It doesn't make any sense, I have stayed true to the plan and even added a new activity in.  I am drinking two shakes and eating one low carb meal a day with celery and water as my snacks.  What gives?!?!  I only have 5 weeks left to lose 25 pounds and this morning I am just not feeling like I can do it.  I still did my elliptical and I still packed my shakes and veggies but the inspired, I can do this attitude has faded a bit.  I am going to email my nutritionist and ask her what she thinks I should do.  I can tell this is going to be a crappy mood day.