Will a cracked tooth filling upset your stomach?

Unlikely: Depending on how deep the crack goes, you may need a replacement filling, you may need a crown, you may need a root canal and crown, or you may need to have the tooth taken out. Even a very deep crack is unlikely to cause an upset stomach although any infection associated with the cracked tooth may cause other problems. Best to see your dentist.

no: Bacteria can enter and cause more decay and lead to an abscess.See your dentist or you may lose your tooth.

Not likely, but : is a possibility. The bacteria from an infected gums travels through the blood stream to other areas/organs of the body can cause bacteremia (bacteria in the blood) can also make you generally ill. With a good oral hygiene, brushing, flossing and professional cleaning this will never happen.