I would say an average of 1500 cals a day is probably good for you. You don't necessarily have to get all precise with it in calculating what exercise you did that day and then making yourself up a food budget (though some people prefer to do it that way) - you could just say 'everyday I should eat between 1400 and 1500 calories', going no lower than 1400 and no higher than 1500, and making sure you're getting some light exercise like walks throughout the week.
I'd second Minnie's comment that you're possibly retaining water. Weight can be so wonky sometimes. Also it's evident that you're already doing this but the key to fat loss is many small meals throughout the day - again, I know you already do this and that IBS-wise you probably don't let yourself get hungry or stuff your face at one sitting when you do - but that's a key to fat loss too, not only staying stable! (Another great thing about this diet!)
I wouldn't worry too much about it right now. See how you are next week I guess.