What causes red streaks up the arm where IV fluids were given?

Lymphangitis. Lymphangitis is infection along lymphatic vessels, usually following skin trauma. It typically tracks from the site of injury toward the torso. It is likely that bacteria got into the IV site and caused a skin infection which develops into this condition. It's very important that you talk to your doctor and get this examined. If it is lymphangitis, you may need antibiotic treatment.