I usually get pain in my left leg but recently I've had pain in my calf and sometimes in my thigh for 3 days now. I'm worried it's a clot and It's too late at night to go to quick care or my doctor. I could go to the ER but I don't know if I even have a serious problem. I don't know what a blood clot would feel like so I don't know what it is. How do I know if this is serious or not?