Constipation for a few days is not a big concern, in and of itself. It might not feel great, but can usually be managed with several alternatives, and shouldn't cause any long-term damage.

After you are bunged up though, it is quite common to experience the runs. Basically the piping gets backed up, and when the stop-gap is removed, everything that was in the piping will come out (often in full force).

The blood . . . is it likely from a small lesion, ie. from straining, or does the blood seem to be coming from internally?

If you are passing blood (not just spotting from external), combined with the runs, you should be checked out. Ulcerative colitis can cause all the symptoms you are describing; abdominal pain, the runs, and bleeding (internally). It is highly unlikely, but if that is it, you'll have a better idea within a few days.

Don't leave internal bleeding unchecked.

Cherie