I have had this medium size lump on the back of my neck for 2+weeks now and I have now been feeling weak having sweats and hot flushes. I have been feeling dizzy throughout the days also. I have also now had black poo. The lump is hard and it does not move at all. It’s on the right hand side on the back of my neck near the hairline. There is also red marks near the bottom of my hairline also. What does this mean? Thanks.