About a week ago I noticed a I had a lump on my left arm, it didn’t hurt and if I pressed on it it only felt slightly tender like a bruise. About a day or so later I noticed the lump had decreased in size and about 2-3 days later it had nearly ceased but the area surrounding the lump was now discolored like a bruise or possibly infected skin. It’s been this way since and hasn’t changed. I’m not sure what it is but I am worried about it.