Nope! I've gone up as much as 3lbs in a day, and I absolutely did not eat 3lbs of food--your body fluctuates throughout the day as a normal part of life. Absolutely nothing to worry about
Definitely only stick to a once per week weigh in though. I know some who will weigh themselves every day, and I wouldn't be able to handle it. I think I'm a touch OCD (I prefer CDO because the letters are in order...), and if I saw my weight going up and down so much, it would give me a heart attack. Once a week gives more of an average, and it's less emotionally exhausting!