Im sorry you are going through a rough time.
Last month i was feeling the same way, i was constipated for 5 days and by the 5th day i was in pain! I dont take any fiber supplements because ive been told that in the long run, your digestive system becomes lazy and will depend on the fiber supplement to function properly. What works great for me is eating fiber one cereal, prunes, and lots of water.
Highly suggest you to try it and let me know how it goes.
Hope you feel better soon.