I took magnesium citrate liquid for constipation, my diarrhea is now a yellowish color (which i think means im cleared out) but i still feel an uncomfortable pressure in my rectum, it makes me feel like i have to go to the bathroom. what could it be?

Passing yellowish loose liquid after taking magnesium citrate does not always mean the constipation has been relieved. You have to pass a lot of fecal materials along with watery stool for defining the effectiveness. Fecal impaction can cause the sx you feel, because the liquid stool goes around the impacted stool. If you truly passed out a lot of feces, do a warm sitz bath for that feeling.