Recently, Both Of My Upper Arms (from Right Below Shoulder

Recently, both of my upper arms (from right below shoulder down to elbow) were red - like a rash, but there is no itching or burning, etc. The strangest part is that along with the redness, my arms feel heavy or tired. It feels as if I just had a workout and my arms are sore/heavy from a workout. My doctor is baffled from this. He sent me for 2 different ultrasounds to check for a blood clot, but it came back negative.