DynamoDB - The security token included in the request is expired

I am attempting to save a bit of info to my DynamoDB Table. The table has been created already, but I received the following error.

Caused by: com.amazonaws.AmazonServiceException: The security token included in the 
request is expired (Service: AmazonDynamoDBv2; Status Code: 400; Error Code:     
ExpiredTokenException; Request ID: MA87ST04UPA57CMUJQIS8DBS4FVV4KQNSO5AEMVJF66Q9ASUAAJG)

It's worth noting that I managed to get the info to save once, but it no longer saves after that first time.

Here's my code.

public class SignUp extends Activity {

@Override
protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);

    setContentView(R.layout.test);

    if (android.os.Build.VERSION.SDK_INT > 9) {
        StrictMode.ThreadPolicy policy = new StrictMode.ThreadPolicy.Builder().permitAll().build();
        StrictMode.setThreadPolicy(policy);
    }
}

public void signUp(View view){
    CognitoCachingCredentialsProvider cognitoProvider = new CognitoCachingCredentialsProvider(
            this,    // get the context for the current activity
            "us-east-1:a8c18251-d7cd-4d56-bcf1-9dd9ccfbf1f0",    /* Identity Pool ID */
            Regions.US_EAST_1           /* Region */
    );

    AmazonDynamoDBClient ddbClient = new AmazonDynamoDBClient(cognitoProvider);

    DynamoDBMapper mapper = new DynamoDBMapper(ddbClient);

    TextView name = (TextView)findViewById(R.id.Name);
    TextView email = (TextView)findViewById(R.id.email);
    TextView username = (TextView)findViewById(R.id.username);
    TextView password = (TextView)findViewById(R.id.password);
    TextView phone = (TextView)findViewById(R.id.phone);

    UserInfo userInfo = new UserInfo();
    userInfo.setName(name.getText().toString());
    userInfo.setEmail(email.getText().toString());
    userInfo.setUsername(username.getText().toString());
    userInfo.setPassword(password.getText().toString());
    userInfo.setPhone(phone.getText().toString());

    mapper.save(userInfo);

    Toast.makeText(this, "Finished!", Toast.LENGTH_LONG).show();

}
}

All help is appreciated.