Frequent blood clot/ bruises. Helpful.

Hi Dr, I get frequent blood clotting or bruises (not exactly sure) on my legs even if I walk for 5 mins without any physical injury.. it starts with severe leg/calf pain followed by red or blue black patches on my legs which resemble blood clots or bruises.. most of the times they r on the thighs (above the knee), mostly on 1 one leg but the pain remains on both legs.. after a couple of days from when these marks appear, I have noticed in the last 3 or times, I have landed with extreme pain in the sternum(the bone between my rib cage) then the pain and pressure spreads to one side of the chest mainly the center which pains when breathing. Do I need to be concerned and wht could b the probable causes.. if anyone has any idea it will be really helpful.. Thnk u for ur help in advance.