Your cover letter and resume should highlight the skills and experience you bring to the table, not what you want out of a job. You're not begging to be hired, you're telling employers why they need to hire you and what they'll get out of hiring you.
Confidence and positivity are two of the most important things you need when job searching. It's easy to get discouraged and become jaded, but you have to catch yourself and switch back into positive thinking. Go on Youtube and watch a clip of your favorite comedy skit, or search "funny animals". Do something to laugh and the go back to applying for jobs, because no one wants to hire someone who seems negative or desperate.
What do you do to stay positive? Let me know in the comments! :)