Just found this thread, as this started happening to me several days ago. Maybe five times or so a day, my inner lower left leg (like by my calf) feels really warm and it lasts for maybe a minute or so.
I'm 20 and not on any meds (except allergy medication and birth control). I'm going to start actually taking my vitamins so we'll see if that helps.
Hopefully it's nothing to worry about...but I'm amazed that so many people have been posting on this thread for so many years now and no answer as to what it is!
Update (part 1):
Went to the doctor, but sadly this wasn't my normal doctor and I don't know if I trust this woman or not. But regardless, she says she doesn't think it's a blood clot (I thought it might be due to several posts here & a google search) because there is no pain or swelling (but it could potentially still be a blood clot). She had me get blood work done, so we'll see what the results are in a few days. She also said to stop taking my oral birth control as a precautionary method..
Does anyone else have an update?