Why sometimes when I have to go to the bathroom so bad and I poop only small amounts the size of pebbles?

Then I feel relieved. Only 1-3 pieces of those sizes come out, and I say how come I needed to go so badly just for that. It is annoying when it happens because it affects me at work and college/school and I might go poop 5-8 times a day small pieces. It is weirder than diarrhea or constipation. Is there a medical term for what is happening to me?