to me, it sounds like you have some symptoms of TMJD, but make sure that other disorders that mimic TMJD are ruled out.. just to be on the safe side.
my symptoms have gotten worse and have changed over the years. when i first started to have problems, i mainly had headaches and migraines.
make sure that you dont do anything irreversible when you start your treatment. it's always better to start out conservative and do reversible things. also, multiple opinions from dentists is always a good idea.
what type of splint are you getting? what other therapies are you trying?