hello, there are many cause of varicose vein like standing job for long periods of time, pressure on the midsection of the body, especially the abdomen,chronic constipation can cause left side lower limb varicose vein, obesity, which adds weight to the body and increases the pressure on the legs, can be congenital , post DVT , abdominal lump which compress IVC etc varicose vein develop when there is reverse abnormal flow of blood from deep venous system to superficial venous system due to incompetent valves so low pressure vein now under high pressure tension and get elongated torturous and dilated get a colour doppler of your lower limb for your venous system , USG abdomen to ruleout any intraabdominal lump etc and consult your doctor as varicose vein is a progressive disease if not treated