Hi. Varicose veins in legs in your case may be due to various factors. First, the hormones which are being secreted in the pregnancy causes dilatation of the veins and so all veins throughout the body seems to become engorged, dilated and tortuous. Second, the increase in the fetal and uterine size put pressure over the abdominal vessels like inferior vena cava and obstructs the flow of the blood back from limbs towards the heart. We cannot do anything to regulate the hormone status, because it is physiological. But, to increase the venous return, a lateral decubitus on lying down will help you. Third, you are saying that you have pain in the leg, that may be due to either prolonged stasis of venous blood in the leg and can be sorted out by lateral decubitus or it can be due to superficial thrombophlebitis which presents as redness and pain for which you can apply heparin gel locally. Apart from all this, please apply crappe bandage over both the lower limbs starting from toe to the thigh and remove it, every 2-3 hourly for 5-10 min and re-apply. Usually, the condition will resolve as the pregnancy is over in just few days. It has nothing to with previous knee surgery and usually, prolonged standing causes worsening of varicose veins and not the sitting. Hope, you get well soon.