It's been a few weeks since my first comment about this and just wanted to give an update in light of your reply in case it helps you at all. I never went in for the CT Scan but I had an X-ray done at an urgent care. The X-ray actually showed a severe fecal blockage indicating constipation, so it turns out that's what it was for me.
I will say that I've never had constipation that bad before in my life and it lasted over a week before I saw any improvement at all. I do think the plan B may have been the culprit as some of what I've read online does list possible side effects of constipation (though I can't confirm the reliability of the sources and I'm not a doctor).
If you think yours might also be bad constipation I would highly recommend eating one or two cups of yogurt a day. I ate yogurt, granola, and fruit regularly for about a week and it definitely helped (I was able to use the restroom after every time I ate it, and even though the constipation took a while to clear up completely, the daily bowel movements after eating the yogurt helped relieve some of the pain little by little).
Hope this helps and hope you feel better!