What Causes Tiny Red Bumps On My Arms And Hands?

I have tiny red bumps on my arms and hands, and the only thing i can think of is, i was exposed to sunlight today after a very long cold winter - could the sunlight have anything to do with the tiny spots? I am a 19 year old female, my weight is around 86 - 90 kgs, and I am about 5 foot 6". I have already had chicken pox, vaccinated agains measels but these little bumps don't look like measels