2001 Dodge Dakota Front Brake Heating/Dragging?

I changed the pads on my front brakes in December. I noticed they were dragging and heating up about a month ago. I took it apart again, cleaned it all up (pads were fine since they were almost new) and put it back together. Yesterday I noticed it was heating up (too hot to touch the rim on the driver side front so I haven't touched it since yesterday. I am wondering what is causing the brakes to heat up? Are they dragging on the rotor and or is the Master cylinder not functioning correctly? I am trying to determine what is causing this heating up of the brakes.