Hi Mindi,
Is it possible that the weight gain would be water retention? (Do your rings feel tighter than normal, do your socks leave marks in the skin, do you just feel bloated?). This could be caused by a number of reasons, which I'm sure you know (that time of the month, too much salt, too little water etc.). Eating too little protein for an extended period of time can also cause water retention (especially when doing strenuous exercise at the same time), as can the deficiency of some vitamins/nutrients. So if you've been on a strict diet for some time, could this be the case? Please be sure you eat enough, it doesn't sound like your daily intake is very high.
I have also recently lost some weight, and am finally pretty much at my goal weight-wise. The closer I got to my goal, the slower the pounds came off, and the more my weight would fluctuate from one day to the next (sometimes it gets frustrating to keep telling yourself you don't gain up to 3-4 pounds fat overnight!!!). In my case at least, I seem to retain water really easy (3-4 pounds is normal around that time of the month), and eating too little (especially protein) would show up on the scale within a few days as a similar gain! Perhaps the body is trying to hang on to anything (even water!) rather than giving up the fat stores..

)! I don't know, but the water will eventually leave, so hang in there. Meanwhie, make sure you eat enough healthy foods and protein to stay healthy! The closer you are to your goal, the slower the pounds usually come off, but remember 1 pound takes about 3500 EXTRA calories, so unless you've consumed about 3 times that, the 1,5 gain is not fat!!! The scale can be a really bad companion to dieting..., I know I am prone to letting it affect my mood too much, even if I should know better...

)
Anyway, hope some of this is helpful, let us know how it's going. It always helps to know weight fluctuations are really common and normal (to some extent, of course), and seldom do they mean actual weight gain (that we wouldn't know or have a clue about).
Hang in there, and enjoy your week,
Maria