Skin Discoloration and Other

Hi, i've been getting weird patches that look like purple blue-ish black-ish bruises
on my arm and near my arm pit  also just under my rib cage in the middle of both of them.. it sometimes is  darker but fades a little but i can still see it there.

also  for a couple of years now  my feet , wrists and palms  and sometimes my nails go dark blue-black-purple sometimes it doesnt matter if i'm standing or siting ,  it also happens in the shower.. it just happens  randomly.. but it always seems to fade away by its self.. after a few minutes, this is what scares me the most as i dont understand what causes it and its much darker looking then the patches of discolored skin i have. i tried talking to my doctor about it but she just shruged and said it might be a small circulation problem and nothing to worry about it (i'm 24 years old (but i've had this since late teens) and 5'9 she thinks its because of my height).. but she hasnt seen it with her own eyes yet(since it comes and goes).. the color is very alarming when it happens, and its definetly not normal, because no one in my family has ever had this problem or anyone i know.. the only thing i've been diagnosed as having is semi low platelets ..but not low enough  for them to give me anything for it.