I have IBS, with constipation. Never had problems lke this.

Now, i get dirrahea or loose stools close to it 1-5 times a day.
It calmed down when i cut some fiber out, so i slowly put it back up and now it's back again. and it burns after a bowel movement, can anyone figure out why? How can I fix this? It's disturbing my life. I think my dad has the same problem.