4th week failure

OK so this week was not my best week! I have been doing my diet for about 4 weeks now and last week when I weighed myself I had lost 5lbs. But, the other day I weighted myself and I gained 2lbs. What the heck is that about! I haven't been eating junk food and if I eat any more greens and chicken I think I will either turn into broccoli or a chicken. So by seeing that I gained 2lbs, which was actually because of "the time of the month", I began eating all types of food, and not worried about the calories or nutritional facts. For example of Valentine's Day my boyfriend took me to a restaurant. But instead of eating a salad with a diet soda, I had steak with loaded mash potatoes and bread..tons of bread. Although I fucked up, I'm not going to kill myself over it. I will just work extra hard next week. Wish me luck!