What Causes Swelling On The Left Side Of Clavical Bone?

I continue to get moments of odd swelling on the left side of my clavical bone . The soft spot on your neck directly blow the ear where your shoulder meets the neck.. It swell up with what looks like blood . I say it because it looks bruised yellow , bluest color as it swells. Now, I get pain down the left arm. My doctor has run test . Thought maybe sub clavical steal syndrome.. But now has ruled it out and unsure what is going on.