You got a flu shot over 2 weeks ago and your arm is still sore?

It sounds like the muscle is irritated. Typically, ice or a cool cloth used immediately after the flu shot can reduce any soreness. However, when it is more than 48 to 72 hours after the injection, you will need to switch to moist heat. You can use a washcloth soaked in hot water-- keep it folded, wet it, wring out the excess water, and lay it on the site for 10-15 minutes. Remove if too hot and try again in a minute or two. OR you can put a heating pad on low heat and put it on the site for 10-15 minutes. You can repeat either method every 4 to 6 hours as needed. If the heat does not help, or you have a lump under the skin or any hard area under the arm, see your doctor.