Yes, the balance definitely needs to be reworked. It's quite a challenge to make the game fun, engaging, and somewhat realistic all at once.
At the moment, there are 144 belly stages (images), but theoretically, you could keep playing forever. ^.~ The limitation through contracts is intentional by design. In the future, I plan to implement a 'Reputation' system, where your decisions and actions will influence both the quantity and quality of available contracts (trips to the hospital reduce your Reputation for example).