What could the cause of a soft lump around my collar bone?

[kevin_2111]

I'm a 16 year old male and I've had this soft lump around 1 inches or 2.5 cm wide right above my collar bone or around the "inferior belly of omohyoid muscle" for almost a year now. Don't think there have been any growth. when i look into the mirror, my right collar bone isn't as obvious as my left right side almost looks flat. but nothing pops up. when i press the lump, it is movable and soft , it does not hurt and i can fell my pulse beating under it. also the trapezius/ neck muscle on the side of the lump, the right side feels very tight and uncomfortable, and when i tilt my head towards the left, you can see a bunch of string like things popping up under the skins and its under tension. When i tried to press the strings hard, it hurts.
Can someone please tell me what it is? and is it serious?
thank you very much