Why I feel dizzy sometimes after bowel movement? Olso my poop is light colored and soft allmost a year now. What could be cause of all that?

Dizziness. Moving bowels causes a parasympathetic nervous system discharge which dilates smooth muscle, among other things, and leads to a feeling of lightheadedness, almost like fainting. As for your lighter/softer bowels not my area of practice but could be a function of diet but should check for infectious or metabolic causes. Go see your primary.