Hi Catherine. If there is no obvious strain or injury then you may need to consider conditions like peripheral vascular disease. The artery supplying blood to the leg may be narrowed and this elicits pain under certain conditions. Similarly the veins of the leg may be a problem, like if there is a blood clot (deep vein thrombosis / DVT). Your history of high blood pressure and hypothyroidism can be contributing factors to these conditions. You may want to speak to your doctor about a special type of ultrasound that will assess the blood flow through your legs. Your doctor will be able to advise you accordingly. Remember that nerve problems can also cause similar symptoms.