Why is the bank postponing financing for my house?

I received approval to purchase a home. I have done everything I have been asked to do to this point. The inspection is complete. I was told a month and a half ago that I need to show a higher balance in my checking account to demonstrate "stability". My ex-husband gave me $3000.00 to deposit in my account to reimburse me for child care expenses. Now the bank want to know where this money came from and they are holding up the process of me closing on my home. I deposited the funds in the form of two money orders. Why is the bank being so stubborn? Is this normal?