The best source of that information is from the originator of the loan. He or she can tell you if the loan was underwritten to Fannie Mae or Freddie Mac guidelines. If you had a conventional mortgage, that is NOT a subprime or government loan, or a loan exceeding conventional conforming loan limits [$417,000], it is likely that Fannie or Freddie purchased the loan. There are some instances when temporary higher limits were in place. So, you will need to check your loan documents for that information.
Another source of that information is the servicer of your loan. This is to whom you make your monthly payments. Your loan should be coded into their system, which should give the servicer a quick read on the purchaser of the loan.
Some new programs are coming out for refinancing options for both Freddie Mac & Fannie Mae loans, so it is a good idea to find out now about your loan. It can save you some time if and when you decide to pursue a refinancing option.