pooing/peeing in the house AGAIN

[jinx]

Recently my puppy has started acting up again and started pooing and peeing in the house even though he's been housetrained. I've actually trained him to ring a bell whenever he wishes to pee as well and he has been doing exactly that for the past, almost 3 months, but recently though he does still occasionally signal that he wishes to pee outside by ringing the bell, more often he pees and poos in the house. What's wrong and how do i get him to stop?

also, on another completely diffferent topic, i was wondering how i could teach him to play fetch? My puppy is very active and energetic and i feel bad not being able to give him daily walks or give him the amount of exercise he needs, so i was thinking by teaching him how to play fetch i can help him burn off more energy in a shorter amount of time, rather than long walks which i don't have much time for~