Most likely, 2 things. Either your brake system is dirty and needs cleaning, or the pads are not seated square and are at and angle causing binding.
Either way, a cleaning is probably in order just because of the DOT3 fluid.
Remove the calipers and pull out the pads. Use the lever to push out the pistons as far as possible without any of them popping off. You should be able to pull them out fairly easy then and drain the brake fluid from the system including the master.
Every piston has a rubber o-ring in it that is a square shape, use a pick to gently remove these. This groove will most certainly need to be cleaned out. There is no straight up easy way to do this but a dremel brass brush wheel makes it pretty quick. A soft metal brush is needed though, a nylon bristle is not strong enough to get the built up crud out and a harder brush may cause damage if a person is not very careful.
Basically, clean the whole caliper of any buildup you ind. If you see anything white or a dusty, clean it. Pay special attention to those grooves though.
Then, clean the master. You will need a snap ring pliers to get out the cir-clip so the piston can be removed. This will need a cleaning too. clean the whole master, make sure you get the 2 holes at the bottom, especially the small hole. A blockage here will cause the brakes to bind.
Once all clean, assemble everything back together. You CAN use a brake grease on the back and sides of the pads, on the metal plates, do NOT get any on the pad surface or you have basically junked them. Grease contaminates the surface and causes poor braking.
Make sure the pads are square. Mount everything and make sure the bleed screws are tight.
Fill the master and open 1 bleed screw and start the fluid fill process on 1 side. Once you get fluid out of the caliper, close that bleed and open the other one. Get that side filled and you are ready to start the bleed process.
Some people will hook a hose to the caliper and use a pump or something to force fluid into the calipers first and up the line. You can try this method if you want.
The ride IS the adventure. The destination is just to get gas!