I have a large lump on my neck near my collerbone which is painful an appeared suddenly, my neck is also stiff an sore what could this be?

Lump: Check with orthopedic surgeon. It could be a-c or s-c joint sprain or dislocation, muscle tear or strain.

Lymph node: Probably a painful and swollen lymph node. I would watch it and if it gets larger may want to seek medical attention. Painless masses or lymph nodes are a bit more worrisome.

Monitoring Centers: Lymphatic system absorbs/carries things too big to go into the arteries/veins like bacteria eaten by white cells and digested food. Lymph nodes "taste" the lymph for anything bad like bacteria/viruses/cancers, etc. When it detects a problem, it alerts the immune system and your body reacts. They enlarge in response to the inflammation they create when they react. They shrink when all is well.