I have a DVT in my shoulder. What exactly causes the pain in my arm? And what exactly would cause weakness in my thumb and index finger?

Thought. Dvt is in the subclavian or axillary veins most likely. Shoulder is a joint and area. Swelling is uncomfortable. Rest, elevation, ace wraps may help control/ decrease the swelling while collateral veins develop. Radial nerve controls thumb and index and may have pressure. Other? What led to the dvt? Surgery, hospital, ? Pressure from brace etc?.
Swelling? Dvt usually causes some swelling which can press on nerves or muscles. Gosh i wish you had mentioned what caused the arm dvt, so we could understand the case better.