I Have Had Unexplained Bruising In A Vein In The

I have had unexplained bruising in a vein in the back of my hand for a few days now.It looks like the vein is bulging slightly.I now have pain in my hand & tingling.I went to my local A&E dept.last evening & it took 5 minutes for the doctor to inform me there isn't anything wrong with it.Well there clearly is as it's just got me out of bed again.What could it be?