Bootstrap-4 Vertical Navbar Stuck Collapsed

I'm just starting to get to grips with bootstrap.

I'm trying to create a vertical-navbar on the left of the page after the user has scrolled past the full-page 'intro' using bootstrap 4. The code below produces the navbar on the left side of the page, however there are two problems with it:

• 1: The navbar stays in a collapsed state, even after resizing the window small and large again
• 2: After resizing it to a small enough state to where it should collapse, the navbar does not become a fixed position navbar (as I would expect it to)

Why does the code start with the navbar closed?

Thanks, Jeff

<header id="home" class="jumbotron h-100vw w-100vw">
...
</header>
<div class="container-fluid">
<div class="row">
    <div class="col-md-2">
        <nav class="navbar navbar-expand-md navbar-light">

            <a class="navbar-brand" href="#home">
                <img src="img/logo.png" class="img-fluid" alt="Home">
            </a>

            <button class="navbar-toggler" type="button" data-toggle="collapse" data-target="#nav-content" aria-controls="nav-content"
                aria-expanded="false" aria-label="Toggle navigation">
                <span class="navbar-toggler-icon"></span>
            </button>

            <div class="collapse navbar-collapse-md flex-column" id="nav-content">
                <ul class="navbar-nav">
                    <li class="nav-item">
                        <a class="nav-link" href="#about"></a>About Me</a>
                    </li>
                    <li class="nav-item">
                        <a class="nav-link" href="#work">My Work</a>
                    </li>
                    <li class="nav-item">
                        <a class="nav-link" href="#connect">Stay Connected</a>
                    </li>
                    <li class="nav-item">
                        <a class="nav-link" href="#contact">Get In Touch</a>
                    </li>
                </ul>
            </div>
        </nav>
    </div>

    <main class="col-md-10">
        REST OF MY CONTENT ON THE RIGHT
    </main>
</div>