Check your nutrition
I agree that it might be water retention, due to that time of the month, or possibly because of high salt intake.
I'd advise taking a look at what you've been eating to ensure that you're getting the right nutrition. Are you taking in adequate protein, vitamins, and minerals? Your body might be stalled, health-wise, because it's not getting what it needs.
Another idea is to switch up your exercise routine. That can help you get off a plateau.
Also sleep. From a lot of things I've read recently, sleep is essential to weight loss. The rest is necessary to recharge the body and let it do what it needs to.
Just like dealing with the stock market, be patient and sensible and don't let your emotions rule you during fluctuations. Slow and steady wins the race!