What Could Cause Unexplained Bruise On Arms Which Looks Dark Brown & Uneven Patches?

hi i have unexplained bruising on my arms which turn into dark brown and irregular patches. last night i had a bruise up most of my arm that was blue green and unexplained within litterally five minutes into had turned brown with the upper portion bright dark red. the bruises that later turn into patches are all over my lower arms now. they only started a week ago. also i have been very very lethargic even after a good nights rest. i am verey breathless and a lump at the top of my neck often causes excrutiating headaches. under my arms but not the lymph nodes is a very painful to touch lump. please help.