Hi
Have you tried to start a session with your main OS drive only as that WD My passport is not what one would recommend even though it's USB3. Those drives are most certain 5400 rpm or less and they could have some form of "green" power saving mgnt so i would either get something that works well with PT and make a backup of that drive and then maybe use it as a back-up at most. Not have anything to do with recording at all.
Try disconnecting that harddrive and start a new session OR import/move one of your sessions to the SSD drive and try PT with WD out of the picture,
What happens then? As you are using that for recording means it is used for saving and reading to and from so that drive might very well be a part of your issues here.
Also there is a host of stuff for optimization and trouble shooting to do aswell here
http://duc.avid.com/showthread.php?t=300050 and make sure you do everything and everything before doing anything drastic. No bluetooth on, no network on, trashing preferences, dae folder, volumes, plist, databases etc.
Very important to do as that is almost always some sort of culprit even though you think those small things doesn't matter, do them ALL
Best Wishes
Christopher