Insect sting makes line of small spots on arm?

I wouldn't be as concerned with what bit you as much as what exactly is happening! It sounds like it has only gotten worse in time and there is discoloration and pain, more than enough cause to seek medical advice. If that is not possible I would use Hydrocortisone cream and/or Benadryl cream to see if that makes symptoms dissipate. However I would suggest getting that checked out if they don't go away soon because that sounds very odd in nature...