HIVES THAT WONT GO AWAY

Oh my god I have hives all over me and they itch so bad, I took a shower and it's still not going away. I took Benadryl but I have no idea what's causing this and it doesn't seem to help I have it ALL OVER ME 
WHAT CAN HELP 
This is day two of breaking out in hives all over my body, they go away and come back within minutes 
This is what it starts as and then it spreads, goes away and comes back again