Given that you have kids, do you ever drink red drinks like Kool-Aid, punch, red fruit juices or cherry fountain sodas? I have definitely found that red drinks will make for red stools (Kool-Aid Tropical Punch being the worst), and it's most noticable when you have only partially-formed stools. Bloody stools are usually dark/black and bloody hemmroids usually bright red (with blood on the toilet paper). If you drink Kool-Aid and you have Kool-Aid colored poop, then it's probably just Kool-Aid. Although colored drinks are the worse, any food that has a lot of red dye in it can do the same thing.
Is your constipation timed to your period? Most of the women on here have some sort of worsening of their IBS when it gets to be "that time of the month". When I was a teen, I always got a bit more constipated right before my period. If you can learn the timing of your constipation, then you might want to try heading it off with some extra fiber, prune juice or aloe vera pills. You might also want to stay away from bananas, cheese and other foods that can worsen or cause constipation.
If this is the only time that you've had this level of pain with a bowel movement after your gall bladder removal, then I wouldn't put you down for IBS just yet (thank goodness, you say!). I've had a few bouts myself of a constipated stool followed immediately by a watery or bile diarrhea stool. If you frequently have stools that are loose or watery with yellow, burning bile in them, then there is medicine out there to help (Welchol). Other than that, I would just chalk this up to a temporary and somewhat random bowel movement caused perhaps, in part, by your lack of gall bladder.