You need to file the FBAR reports for the years that you did not file but should have. You will have an opportunity on the report to indicate why you are late filing the returns, there will be a list of reasons to choose from or you can type in your reason if you don't find one that fits your circumstance. Here is some information on the subject from the IRS: FBAR reporting
I believe by unrealized gains or losses you mean you have purchased foreign securities and they have gone up or down in value but you haven't sold them yet. Those changes in value are not taxable. You only recognize gains or losses for tax purposes when you dispose of the investment.