I agree with PPs. I think trying to PTing now will worsen the issue. I would try miralax and consult with a different pedi or specialist. I'm not doubting the seriousness of the issue, as I know constipation can turn serious quickly and cause a lot of problems (we dealt with it recently too), but I think you should try miralax and a change in diet first. I just think the pressure to PT especially when there's already a constipation issue will just make things worse and mix up your DC.