Tomorrow you get: B A N N E D for disclosing confidential information about your stats.. anyway.. what you're seeing is SmartPricing.. happens to the best of us..
random observation: your ads suck Your money fluctuates based on the value of the ads being displayed. Some days Google is generous, other days, not so much. If your pages invite expensive keywords then your day to day income will fluctuate but at a higher min and max. What you need to do is rework your content.