insect sting makes line of small spots on arm?

Yesterday morning I was stung/bit by an insect of some kind, I brushed it off so fast I didn't see what it was. I assumed it was a bee or wasp, well, because that is what it felt like. But the original red bite spot has spread into a thin line about 2 inches long down my arm. It is in the appearence of little dark brown, slightly recessed spots. I can feel a slightly aching pain along the whole line.

I've never had a flying insect sting that looked like this (generally those just stay a red spot in one place) I have been researching and spider bites don't generally have pain until after a while, so I cannot figure out what bit me! I've looked and looked on the web for stings in this pattern but I cannot find anything, any idea???