I had a blood clot in my leg that started in my calf. I have had cramps before that were just that, cramps. But with the clot that I had, it was a very different kind of pain, more intense that just came out of nowhere. It woke me up in the middle of the night. I never had any of that burning sensation that others have said they had, but the biggest problem was that my whole leg was weak and was swollen. I did not know that I had a clot in my leg, and didn't get it checked out until almost 2 weeks after it formed. By that time I had a solid clot that runs from below my knee into my pelvis.
My best advice is to call your doctor. If you are on birth control, it is always a possibility that you might have a clot. If your symptoms have just come out of nowhere, it might be a clot. There is no harm in talking with your doctor to see what he/she says. I was diagnosed by an ultrasound, and if you have one, they will find it. Best of luck to you! I don't know how helpful this was, but I just wanted to say do not wait to contact your doctor. They will be more helpful than anyone!