I 100% agree with 67drake and 73LeMans. The pads slide in and out in a small track. There is a shim in that track and the pads slide within the shim. A small buildup of rust happens under the shim. This compresses the ends on the pads preventing them from sliding.
Remove the caliper bolts and set it aside. Then remove the bracket that holds the caliper.
If you have a bench vise place it in there.
Take a rough file edge or something similar and clean up that groove that the pads slide in. You can also put some brake grease or small amount of anti seize in the grove before you put the shims back in.
Also just so you know I believe most parts places carry these for about 20 bucks each. They will want your old ones for a core.
I have been through this and I bet this is your issue. Good luck.
Paul