I feel your "pain". I have a genetic condition that predisposes me to clotting. I had no idea that I even had any problems until I had a brainstem stroke last March at the age of 46. Anyway, I feel heaviness and fatigue in my legs at times (actually, most of the time) just like you. I just basically force myself to run through it. I know that's not the encouraging information you were hoping to hear, but I'm afraid it's all I've got.
BTW, my doctor said the same thing about Plavix as yours did. It's great for heart patients, but doesn't work for people like us. He said the only two options are aspirin (only for "first-timers -- once you have a repeat occurrence, aspirin is out) and warfarin (coumadin).