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.
Various. Red streaks may be over your vein and be normal reaction to the IV, however they may also indicate an infection, best check it out with your primary care doctor. Especially so if you also have swelling, warmth, or pain.