Numbness In My Left Arm...

I am a 24 y/o girl, at reasonably good health, and have not previously had this problem. Approximately 30 hours ago I started feeling numb in my left arm, almost in a line from my elbow to the tip of my little finger (not numb in any other fingers). I did not think that much of it at first, since it sometimes happen that an arm or a leg "falls asleep", but after a while I started to wonder why it doesn't go away. I can't remember bumping into anything, and have no sore spots that could indicate that I have hit something in my sleep. Also, I woke up today with a mild headache, and it has been coming and going all through the day.

I did a search on google, and it says that a lack of b-12 vitamin may cause numbness. I do have this problem, but I am getting treatment for it (injection every 3 months) and I haven't experienced anything like this earlier. I am not currently on any medication either.

I should probably mention that I spend most of my days sitting still infront of a computer, although I find my mothers theory about a blood clot a bit far fetched considering my young age and reasonably healthy diet.

I have already decided to contact my doctor on monday if the numbness doesn't go away, but thought I should ask here if it might be prudent to contact the doctor already tomorrow.