Weird lump on my neck..help?

HI..so about 4 days ago i noticed a small..like dime size hard lump on the middle left side of my neck on the inside of my neck.. it doesnt hurt..but when i look in the mirror and turn my head i can see it a little bit..almost like its 3d.. i am really worried.. also i just started a kickboxing cl last week..could this be a knot or something serious??