You might have vine borers, which are small caterpillars that can bore into the fruit or the vine. Look for a small hole. You can stick something into the hole, like a nail, to kill the caterpillar. The fruit may then reach harvest size, providing disease doesn't set in.
Login using the form on the top of the page to post feedback (if you are a registered user). If you have not yet registered, click here to do so. It's FREE!.