Both magnesium and Vitamin C (ascorbic acid version) in large doses can help with constipation. They are often recommended to "bowel tolerance" - until you develop diarrhea.
It's important to be drinking water in ounces that's at least half your body weight.
There's an Ayervedic herbal preparation made from 3 Indian fruits that can provide effective yet gentle relief. It's called Triphala - I've taken Planetary Herbals brand upon recommendation.
Here's some info on it:
www.planetaryherbals.com/products/GP1554/Hoep you feel better soon!!