Red spots all over my leg come and go!

Hi Doctor,

I am a female college student and I am 21 years old. Last fall semester I satrted having these red spots all over my legs (they look like small bites but deep red). They don't itch at all just that they look really ugly. Well, last semester i had these red spots at least twice; i don't know what is the cause of them. This semester I had the same red spots all over my leg at the beginning of January. The red spots were deep red and I had them more in the left leg than in the right one.. Well, the red spots were gone, and now they started appearing today again on my legs. This time I have more red spots in my right leg than in my left one. They don't itch at all, but please tell me what could be the reason of those red spots.

Thanks!