Brief Answer:
Probably a vessels problem.
Detailed Answer:
Hello and thak you for your question.
I read carefully, and understood your concern.
Swelling in the lower part of the leg may be due to some reasons.
The most common cause is a problem with your blood vessels,probably
varicose veins,or even a sever condition called DVT (
Deep Vein Thrombosis ). This conditions shows up eith the symptomes you prescribe.
Anyway, the first and mos important thing to do, is to do an Echo Color Doppler ( Color
Ultra Sound ) of the lower
limbs, to check if there is any problem with your blood vessels,or if there is any presence of trhomb formation that does block the normal blood flow of that leg.
If you have any further question,please feel free to ask again.
Best Regards!