Hello Melanie:
I would eliminate the variable by uninstalling the AV program (use the Symantec uninstaller from their web site). Since there are
NO viruses that affect a Mac running OS X, AV software (IMHO) wastes computing resources and, on occasion, causes problems. If that does not help, we can try other things.
When you get a chance, post your configuration in your profile. That will give everyone base level information.
Barry