Yesterday I noticed this hard, immovable, bony lump on my shoulder. There was no pain associated with it, although I have been carrying a 5.5kg bag on this shoulder pretty much everyday for quite a few years until now. The lump is positioned exactly where the Acromioclavicular Joint (ACJ) is. It can be seen when looking in the mirror and comparing left shoulder with right, although it is not something that I would describe as being very big, or even big at this time. However, it is noticeable. I haven't noticed it before, although it is possible that it has been there before. There is no tenderness upon light touch, if I press hard on it, of course it hurts, but it hurts on the other shoulder as well if I do this on the ACJ. It feels as if the lump is part of the bone. Today I carried my bag on my other shoulder, and I found that it's a lot more painful that way. I think the other shoulder (the one without the lump) isn't used to having heavy objects on it.
I am 22 years old. What are the chances this is bone cancer? If it isn't cancer, what could it be? I've looked at pictures online, and it looks almost identical to ACJ separation/dislocation, except that from my research it doesn't seem like heavy bags can cause this... Also ACJ separation/dislocation seems to be associated with pain too. I will be going to the doctor in the next 2-3 weeks (I can't anytime sooner), so please don't advise me to go to the doctor. Thanks!