I've had the testing a couple times. The first time, I just felt the going was a good thing because you are passing all that Barium out of your system. What you are passing will probably be lighter in color or even whitish...that is the Barium.
I had the opposite problem the second time. I went days without going, which was abnormal for me. I finally went to my GI doc because I was worried and he had me do x-rays which showed nothing was bound up. I actually had to then do a "prep" style cleanse to get the barium to pass through.
I wouldn't worry unless it continues. I wouldn't take any anti-dirrheal unless it is extremely bad because you do want to pass the Barium out of your system.