I will NOT get frustrated!

So on October 19th I started weight watchers. I started weighing in at 219. That is the heaviest i've ever been in my life. Considering when I graduated high school in 2001 I weighed 110 lbs. So in the last 8 years i've gained 100 lbs. OMG!! So the first week I lost 6.8 lbs. Which was awesome. Mostly water weight but awesome. The second week I lost 3.6 lbs. My weigh date is on Mondays. So as of today I've only lost 1.6 lbs for the week. And what is the craziest thing is that i've been walking everyday! I'm really trying not to get frustrated and I know this is normal. I will have off weeks. But it doesn't stop me from feeling like a failure. I graduate from nursing school in May. I figured out that if I lost an average of 3lbs a week i can lose 72 lbs before graduation. That would be AWESOME!! Although at this present moment I'm not feeling very confident about achieving this. I WILL NOT GET FRUSTRATED!