I seriously don't understand how this is possible...?

Last week, I lost about 7 pounds, bringing me down to 224.5 lbs. I biked 7 miles, for maybe 3-4 days of the week. Then, this week, I biked 12 miles, EVERY DAY of the week, and ate no more than about 600-700 calories per day. I even started taking weight loss pills daily. I did my weekly weigh in this morning, after not eating or drinking anything for about 10 hours. I weighed myself at 11 AM, and at 1AM, 10 hours before the weigh in, I ate a single slice of bologna and American cheese sandwich on one of those 100 calorie buns, along with a 45 calorie bottle of gatorade. I thought that if I can lose 7 pounds in one week after barely dieting or exercising, I could lose a ton of weight if I dieted hardcore and biked 12 miles per day. BUT, I actually gained 2 pounds when I weighed in this morning. How could this be if I biked 12 miles daily, took weight loss pills daily, and consumed no more than 700 calories daily?