do you go into IM heavier or lighter?

^^This.  Describes my approach almost 100%.

I know any number of people who ended up gaining unnecessary weight during IM training (a couple of whom DNF'ed).  Generally, that's just fat that isn't particularly helpful, either from a load or a fuel standpoint.  I think there are multiple reasons (huge training loads do play games with your hormones, for starters), but a lot of times people just completely misunderstand the relationship between calories in food and calories burned in training.

I write down everything I take in not just during a long workout, but also before and after.  It can be really eye-opening how many calories you can consume when replenishing after a long ride (on top of what you replaced during the ride) if you actually record them...and then people often still go off with training partners and have unusually large meals (often with lots of alcohol, it being the weekend and all).  Next thing you know, you've managed to replace the 4000-5000 calories you burned on the ride and you're not even done eating for the day.

I pretty much stay within about a 10lb range year-round.  Don't worry about a particular week.  If you're shooting for a certain weight and you're not there yet, then you should probably track your progress over time.  You want to identify the overall trend, not minor ups and downs.

Also weigh yourself at the same time of day, otherwise you get more variation.

My weight fluctuates a good amount during any week (around 5lbs typically) and it's hard for me to get a gauge if I'm actually gaining or losing weight looking at any single day - but I'm able to see trends over a week or so.     

Also, most people I know that set weight loss goals come up with a number that they want to lose for a race and use that as their bible.  Things like:

 - "I used to weigh 180lbs when I played XXX in college, so that's what I want to weigh" or

 - "I've gained 15lbs this year, so I want to lose that before my race".  

 - "I really need to wear a size 4 pair of jeans because that's what my friend wears"

I think those goals are well and good (and provide great motivation!), but they are rooted in emotion - not based on facts or relevant questions like "what is the ideal weight my body wants to weigh to race at my best"?  

I've felt like you do, but usually it subsides in another week or two.  I wouldn't get discouraged!  If you keep on an extra couple pounds, maybe it's additional muscle mass or your body telling you it needs the extra weight to sustain ~55hrs of workouts a month.  

I have read some interesting articles about IM training and how it effects men and women differently.  Sadly often women gain weight IM training where men lose weight and some men struggle to keep weight on. One coach who trained many IM couples who did similar training and ate most meals together, the man would lose weight where women would gain.

In one week you can't gain that much weight. You are doing LP?  If so, your body is likely carrying a big load of fatigue with all your training.  When was your last rest week?