@_@ Assuming you're cisgender, you should not be beating yourself up for gaining a mere five pounds, because it is completely normal for a woman's weight to fluctuate like that. It all has to do with your menstrual cycle.
So since you're saying that, in the span of a month, you lost ten pounds, then gained five? I'd say that both the weight lost and the weight gained were probably nothing more than the result of your body's usual monthly activities. So, the bad news is, I'm not sure you can really credit yourself with losing those ten pounds. But the good news is, you didn't do anything wrong. You don't have to feel bad about gaining that weight back. Also, you're likely to lose those same pounds again next month.
In fact, because of this monthly fluctuation, I would ignore any weight gain/loss that's any less than ten pounds away from the norm. This unfortunately means that you can't get too excited about those moments when your weight is on the decline, but it also means you don't have to worry so much about it going back up again. So, instead of tracking every instance of your weight increasing or decreasing, maybe look at monthly averages instead? Because a regular series of ups and downs is normal, but also doesn't show very much progress in regards to your goal. But if, on average, you see that you weigh less now than you did several months ago? Then you're getting somewhere!
But yeah, don't feel bad about your weight spiking up again in a short amount of time, or the increased appetite that would result in such a weight gain. Your body is literally trying to reconstruct the lining of an organ -- not just for you but also for the potential zygote that would need to latch onto that nutrient-rich lining. Your body needs a few extra calories to pull off that sort of thing. @_@ Also, blood has weight. If you're losing blood then you're losing weight, technically speaking. Just seeing that your weight has gone down doesn't necessarily mean that you've burned any fat, especially in regards to a machine as finicky as the female body. >>
Also, have you ever tried to weigh yourself before pooping, and then weighed yourself again to figure out how much your poop weighed? ...What I'm trying to say is, your menstrual cycle isn't the only bodily function that results in regular ups and downs in your weight that have nothing to do with fat-burning. Your body consumes and expels enough things on a regular basis that you'd need to observe a significant increase/decrease in your weight over a long period of time (several months, at the very least) to really say that you're "gaining/losing weight" in the way that you mean. So, if you're the type of person who assumes that you've done something wrong because you suddenly weigh two pounds more than you did yesterday... I would try to get out of that mindset.
Point is, don't freak out over the little bumps and spikes like this. Such increases are normal and healthy and not at all a sign that your diet isn't working out for you. I recommend looking at long-term changes in weight for a more effective indicator of whether or not you're actually losing weight. And, in general, instead of taking things day-by-day, just try to develop healthier habits that you keep up day after day, regardless of whether you happened to gain or lose a few pounds on any one of those days. Because, if you're adopting healthier habits and sticking to them, then those habits should lead to a healthier weight down the road -- it'll just be a while before you can see any clear signs of it. Regularly re-gaining a few pounds here and there doesn't mean that all is lost, so don't let yourself be fooled. :P