It's important to remember when it comes to firewalls and antivirus, that you can only have one of each type of program running at once. Running multiple programs of each type can cause conflicts that make you less safe.
Unfortunately, not every security suite can catch every threat. That's why your sheriff needs a deputy.
For that I recommend Malwarebytes. It's capable of finding and removing threats that other software misses. Plus, the free version won't conflict with your existing antivirus.
To get started, click the white Free Download button on the Malwarebytes home page.
You'll want to leave the "Update Malwarebytes' Anti-Malware" button checked after install. That way, you'll be sure to get the latest version of the program when it's released.