hi there,the site you have described could be the opening in the thigh for the great saphenous vein
and could be related to the vericose vein that you have plenty of. My suggestion would be to visit a surgeon and get yourself examined to rule out any complecation of varicose vein and also if required get a colour doppler of the lower limbs
done to rule out any deep vein thrombosis
or other complications of varicose veins
. If the the lump is non vascular and hard to feel then an FNAC can be considered to rule out other pathology. You should visit a doctor and get yourself examined and get any opinion if required according to me.Take care.