Swollen Left Leg Lasting For 5 Months Right After Taking

Swollen left leg lasting for 5 months right after taking a 6 hour airplane flight. I have had an mri for my left knee due to a torn meniscus and an x-ray and surgery to fix that I thought that would end the swelling but it hasn't. I also had an ultrasound of my legs because of a couple small varicose veins thinking having them fixed might help but now I'm not sure if I will find help with that surgery. My concern is that I might have a blood clot but so far my heart/vein doc and my knee doc haven't answered why this swelling is here.