Confidence is so hard to come by. I'm not asking if you are a male or female human, but women get all kinds of subtle messages of inadequacy that can really cut down their confidence. That can pile on on top of other company dysfunctions that affect everyone and lead to some nasty -- and unwarranted -- imposter syndrome.
My suggestion is to treat yourself as the PR arm of "Harper, Incorporated," which is a business. You are not promoting yourself, but your business, which is selling your services.
So what would you do for your client, "Harper, Inc."? You'd update and polish the resume, you'd apply for jobs, you'd hustle for them. You would campaign on your client's behalf.
Also -- yeah, networking can be helpful, but you can get where you want to go without it. I got most of my jobs through blind applications, not through networking, and I've done just fine.
So work on your cover-letter and resume skills. Don't worry about being confident, just about pretending to be confident on behalf of your client, because that's your job, and you're good at your job. A little positive spin is fine -- not lying, just presenting your client's best features in a good light.
Remember that sincerity is everything. Once you can fake that, you've got it made. ;)
Good luck.