My top front tooth really hurts! what could it be?

You might have cracked it when biting into something. Keep a close eye on it - if the pain comes back, you'll need to go in to a dentist if you want to keep the tooth. If it's cracked, then that means that food particles and bacteria can get inside and cause an abscess. If that happens, you might not lose just the first tooth but some of the surrounding teeth.