What Causes Constipation Followed By Diarrhoea And Blood In Stool?

I have recently been told I have a 4mm kidney stone and have been taken co codimal & ibruprfen, I am waiting to see a consultant, howvere I have been constipated last evening I had stomach ache in my lower bowl followed by diarrhoea this morning I have had a lots of wind buts also red blood (quite a bit) I am going to see my GP today but am quite frightened.