Why can�t i do a number 2?

hey guys i feel kinda embrassed about this and i no it�s not nice to talk about sorry but i need some info, why is it i don�t do a number 2 for like a week and thwen i get a really bad pain so i go to the bathroom and i can do a number 2 but i can only do it when i get this pain and it�s like every 7 days why is taht? is it serious?? or could my colon be damaged or something?