Macbook Pro left (primary) click not working

Solution 1:

It was my Magic Mouse. I turned it off and the problem was resolved. I had my mouse in a box with some other things that must have accidentally shifted and was pressing on the button. Once I found it and turned the mouse off, everything was fine.

Solution 2:

Does the trackpad click feel normal? Does the trackpad feel recessed or sunken at all?

There are two possibilities here:

1) trackpad needs to be adjusted - there is a little adjustment screw when you take off the bottom case - sometimes it needs to be turned to make better contact with the trackpad. Apple will usually adjust this for free in the store as an attempt to fix the clock issue.

2) the trackpad is failing. What you described is a classic symptom. You might need to have it replaced.

There is a trackpad diagnostic that Apple stores have. Make an appointment and go in. It's free.