Weight gain

Today I got on the scale and realized I had gained 12 lbs within a month, maybe less. I'm not pregnant. I feel so depressed and disgusted.  All I've eaten today is a bagel with peanut butter. I've drank 3 glasses of lemon water and a cup of black coffee. I also worked out a little bit (lunges, push ups, squats, etc) and then I went to work for 4 hours. I'm a hostess at Bob Evans so I'm standing and walking the entire time. I also took 4 Zantrex diet pills today. It is now 11:48pm and I can't sleep and I'm starvingggg but I don't want to eat because it's so bad to eat a night. I'm tired of being fat.  It's so hard to resist. Any advice??