Why the hell is my checking balance negative?

I use Bank of America and the overall checking balance is positive and I know for sure it's positive... but on the list of account activity the latest balance says negative. A 700 dollar difference!!! Nothing on the activity indicates where this 700 dollars went, but instead everything is shifted to accommodate this 700 dollar difference, as if it just disappeared! What is going on!!! I checked my account 2 hours ago and available balance was still fine but I check now and it's gone negative. I don't think anyone stole my card number and used it, because if they withdrew or spent it, it should show in the list of activities as a decrease in 700, but instead every single activity and balance that I had just shifted down 700 dollars!