Please help me i got red spots on my arm and im very worried?

Ok so just now i was brushing my teeth when i noticed i have a patch of red spots on my upper arm I looked at them to see what it was and at first i thought i was leaning against somethinty, but then i went away and they were still there as red as before.It does slightly hurt when i press on the area where they are, i have a strong patch up my upper left arm and on the right there's only a few blunt ones there very tiny, if its any use, i been outside quite a lot today i scratched myself with a fork (by accident). Please help me i get very very worried over things that happen to me so please help