Extremely stressed in graduate school and afraid i'll graduate without a job

I'm a first year graduate student in an applied economics Ph.D. program. It's been a very stressful semester and have felt like I haven't done well. I'm used to doing quite well academically and now I'm a little bit below average. As a result, my self-esteem has been going down and I have no self-confidence in any of my work.

In addition, I am afraid that I will not find a job once I graduate. If I was unable to obtain one lousy internship in undergraduate with a good academic record, how the fuck am I supposed to compete with other Ph.D. students for positions? This anxiety probably stems from, despite applying to 300-400 internships, not getting any positions. I mean fuck, I haven't gotten a call for an internship in 2 years. I really have no idea what to do if this trend continues. My inability of getting a job is a major contributing factor of me staying in the program.

I am sick of being such a loser in very faucet of my life. I don't want to have to be driven by anxiety throughout the day. I just want to be happy for once.