Weight increase with little change in nutrition & exercise?

 Hey all -

     The last week or so I've had a few concerns and was hoping some of you great people can give me a hand...I've tried finding information from other forums and have learned a lot from that, but still have a few questions / special circumstances.

     Currently I'm 6' tall with a runner's build...my weight is what's troubling me a little bit.  For the last year or two I've pretty much only run (about 70 miles a week) and have recently added weight training and swimming to my routine (weight lifting MWF, swimming Tu, Th) as well.  I'm not really trying to lose a massive amount of weight, but just wanted to drop a few pounds before I start racing in a month.  Last week I weighed in around 149lb and had been losing about a pound a week for the previous few weeks.

    However, this week I weighed in and found myself weighing 154lb - I tried weighing at the same time, same condition, properly hydrated, etc etc so I can't figure out where the extra 5 pds came from.  Most days I burn about 1000 calories (again with all the running and exercise I need about 3500-4500...so it's not like I'm eating a single salad for the day) a day - and normally the weekends are break-even or a little bit over (I still like to enjoy a few brews with my mates and run less on the weekend anyways).  I don't know if this extra 5lb can be attributed to muscle gain, which I guess is not highly-likely due to my calorie deficit, or what I can attribute it to.  Any ideas?

   Also, any advice from runners that are working on a similar schedule?  I like being lighter on my feet, but it seems that I've been struggling the last few weeks with my runs and actually running slower than I used to.  Could this be related to the calorie deficit, or perhaps it's just being a bit sore from adding in the other activites and it should breeze over in a week or two?  Thanks for all the help guys...cheers.

don't weigh yourself. You are at a healthy weight. I GAIN a few pounds when training for an Ironman or marathon. Also, if you recently upped your mileage it's probably water weight.  If yur not eating enoug ( 70 mpw is a lot) the body may be holding on to a few pounds.