While you are waiting to get call backs for interviews, why don’t you spend some time researching how to create your own job? I am always amazed by young people these days who have the entire world at their fingertips, and technology and equipment that they could put to use to make money. Do you have any skills or knowledge that you could offer to others? Have you ever taken a look at sites like Fiverr? Have any junk you could sell on eBay? Don’t laugh - selling on eBay can get you some cash, clear the clutter, teach you some people and money and business skills. And why not? Until you have a job, you have plenty of free time.
Do you have a car and could you run errands for people or make deliveries? Do you like computers and do you have any interest in learning how to write code? Sure, it would take some time to develop your skills, and get those skills matched up to money-making opportunities, but you might as well work on this while you wait for an employer to maybe - or maybe not - call you back.
The world has already changed. You are now competing for low skill, entry level, customer service jobs with laid-off Baby Boomers, cash-strapped senior citizens, foreign labor of all kinds, and, as you know, you are at a disadvantage trying to find a summer-only job since I guess you don’t attend college in the same town. Employers have the upper hand these days, and even those who are filling the lowest skill entry level jobs are able to choose from candidates who are way over-qualified for those jobs. However, why get depressed about that? You are already in college, which means you have some level of intellectual skill. Now, just put that proverbial thinking cap on and figure out how you can take what you already know and the skills you already have, and get other people to pay you money for your time and effort. It does not have to be a lot of money - some money is better than no money. If you realize you are lacking some marketable skills, then start getting some skills. You should master customer service skills, applied math skills (knowing how to handle money), and you should master computer software programs. You may use Microsoft Office all of the time - everybody does these days - so push yourself to get certified as an expert user of such software. I just saw a job listing where a business owner was looking for a Microsoft Publisher expert to help him create booklets and advertising. My high school age daughter just used the software to design and publish a book (20 pages, 1000 copies.) While she won’t be applying for that job, she could certainly advertise her services. You can do something similar.
You are going to have to make yourself be a positive thinker, though, and stop looking at the world as if it does not have enough opportunities for you. There are plenty of opportunities, but you are going to have to work a lot harder to get access to them. If you want a regular job, then you should be sending out far more than 15 applications. You need to use a spreadsheet to track your applications, and then follow up with each one. I don’t know that I agree that cover letters are essential. They are nice, and a fine tradition, and more appreciated in some parts of the country than others. Face-to-face is going to work better for these entry level jobs. You need to talk to whomever it is who hires new employees. And you need to use your network of friends to help - most jobs are filled with referrals from current employees. Don’t ever view yourself as being too good for a particular job. At this point, you should be of the mindset that you are open to any job (barring those that go against your personal values.)
Do you have a Goodwill Job Center nearby? You may have never considered accessing their services, but they offer some great job readiness programs and employers hold recruiiting fairs there all the time at the one near me. A big inventory company in my area just held a fair there with on-the-spot hiring.
Anyway, I know the job hunt can be frustrating - job hunts have always been frustrating. It is like fishing - you have to cast a very wide net in order to catch just a couple fish. While you wait for a catch, work on developing those customer service/people skills (plenty of free training available online) and master Microsoft software. If you can do anything with Word or Excel or Access, for example, you might have a really great chance to get an on-campus job in an office at your school.