Lump in the back of my head, should I be worried? (Pic inside)

So, about a year and a half ago I noticed a lump on the left side of my neck (tried to make a picture, and this was the best i could come up with. The lump is about the correct size aswell).

It doesn't hurt, it's kind of hard, but thats about it. The only thing i really feel from it is that it can get a bit tender around the area when I train and move my neck a lot (boxing).

I went to a doctor to try and get it checked out but he said he didn't feel it, and that it most likely was a fatty lump.

I know i shouldnt take medical advice from Reddit, but i'm just curious as to what you guys think. Should I look it up and get it removed? Or is it completely harmless?