Having Issues with Writing Backend Code in Express and Connecting To React

I'm writing a code for creating a group within a website. And I'm using MongoDB as my database, but as a beginner, it's hard for me to understand the API that they provide. So basically, I'm having issues with connecting the backend to the frontend when I'm trying to create a group for my website. This is the backend code for create_group

router.post('/create_group', (req, res) => {
    try {
        const newGroup = Group.create(req.body);

        res.status(201).json({
            data: {
                Groups:
                    newGroup
            }
        });
    } catch (err) {
        res.status(400).json({
            status: 'fail',
            message: err
        });
    }
  //res.json(database.groups[database.groups.length-1]);

As you can see, I want to write a code that's appropriate for MongoDB that looks like the portion that I commented out. I want to return the object that I just saved so I can display that information in when I change the route. The frontend code looks like this:

 onSubmitCreate = () => {
        fetch('http://localhost:3000/groups/create_group', {
            method: 'post',
            headers: { 'Content-Type': 'application/json' },
            body: JSON.stringify({
                name: this.state.name,
                description: this.state.description,
                members: 1,
                likes: 0
            })
        })
            .then(response => response.json())
            .then(group => {
                if (group) {
                    //this.props.loadUser(user);
                    console.log('this is what Im working on' + group.name);
                    this.props.onCreateGroup(group);


                }
            });
    }

In the frontend, as I make a request to post the information to the database, I want to read the response and work with that information. But when I console.log the group variable, I just get an empty object as a response and I don't know how to make it return the information that the user typed in. And in case you want to see what onCreateGroup fucntion looks like, here it is.

    const onCreateGroup = (group) => {
        setGroupInfo({
            name: group.name,
            description: group.description,
            likes: 0,
            members: 1
        });
        setRoute('group_page');
    }

Please help me! Thank you in advance!

Edit: I was requested to post js file where I import express so I'm posting it here

const createError = require('http-errors');
const express = require('express');
const path = require('path');
const cookieParser = require('cookie-parser');
const cors = require('cors');
const bodyParser = require('body-parser');
const logger = require('morgan');
const mongoose = require('mongoose');
mongoose.connect("mongodb+srv://teamboogle:wMKsYJNhTfL89k9@cluster0.nhcrc.mongodb.net/TalkWithMe?retryWrites=true&w=majority", { useNewUrlParser: true });

const indexRouter = require('./routes/index');
const usersRouter = require('./routes/users');
const profileRouter = require('./routes/profile');
const postsRouter = require('./routes/posts');
const groupsRouter = require('./routes/groups');
const signinRouter = require('./routes/signin');
const registerRouter = require('./routes/signin');






var app = express();

app.use(logger('dev'));
app.use(express.json());
app.use(express.urlencoded({ extended: false }));
app.use(cookieParser());
app.use(express.static(path.join(__dirname, 'public')));

app.use(cors());
app.use(bodyParser.json());

app.use('/', indexRouter);
app.use('/users', usersRouter);
app.use('/profile', profileRouter);
app.use('/posts', postsRouter);
app.use('/groups', groupsRouter);
app.use('/signin', signinRouter);
app.use('/register', registerRouter);


// catch 404 and forward to error handler
app.use(function(req, res, next) {
  next(createError(404));
});

// error handler
app.use(function(err, req, res, next) {
  // set locals, only providing error in development
  res.locals.message = err.message;
  res.locals.error = req.app.get('env') === 'development' ? err : {};

  // render the error page
  res.status(err.status || 500);
  res.render('error');
});


const db = mongoose.connection;
db.on('error', console.error.bind(console, 'connection error:'))
db.once('open', function(){
  console.log('Connection Secured');
})

module.exports = app;