What Causes Sudden Pain In Calf With Feeling Of Tourniquet Around Leg?

I stood up and had a sudden pain in the calf on Friday, it is worse when I walk. Today it feels like I have a tourniquet around my leg below the knee. I have had some pains in my upper leg over the past month or so. I do not see any redness or swelling, my leg is not hotter or colder than normal. Wondering what may be wrong, my wife is worried it could be a blood clot.