Mini schnauzer and blood

My Clifford was fine in the morning when I came back from errands he acted weird went outside and when me in I picked up and loved him I got I drop of blood on my finger from his butt. He ate some supper a little he went out and came in I checked his butt and wiped and got blood and later on he threw up and it was his supper. It is like he is trying to poop I went to see were he was and nothing but maybe little bloody mucus. Drinks a little water. Will take a bite of whatever but that is it. Could he be constipated ? His tummy talks big time like upset ! He is 13yrs.