extreme pressure but no excreta and little blood

I have been this problem from the past 24 hours.

I have extreme pressure but when I move to toilet almost no excreta comes out. It seems as if something big is stuck inside, but trying for a few minutes, I realize there's nothing in there so I get up.
This pressure comes every 30-50 minutes.

Moreover, in very small quantity the excreta that comes out contains some blood too.