I am having abdominal pain right below my belly button. I haven't had a bowl movement in a couple
Of days so I took some magnesium citrate. Now I havr
Diherra with blood in it. What should I do?

You should find a walk in clinic for best care, and if there isn't one, go to an ER.
Don't take any more pills meanwhile.
There are too many possible conditions it could be, from mild to serious, to go into them online.