My macbook pro trackpad's right side doesn't go down when pressed
This might sound crazy, but I was having the same issues. I could not figure out what the problem was and it was getting really frustrating. One day I lifted the front and noticed that the battery cover was not flush. So I plugged in the power cord and removed the battery, and I was amazed that the battery was swollen, and in turn not letting the trackpad press down. It was bizzare. 

After removing the battery, the trackpad worked perfectly. I don't know if that is your case, but I will be ordering a new battery. A quick search in the Apple Tech website, and it seems this is a common issue with the MacBook Pro batteries. Hope this helps.