OP, I was in a similar boat for a while.
I graduated with a degree in the social sciences, cumulative GPA under 3.0. I had no internships.
I went through a little period of homelessness this summer (but I was able to couch surf with understanding friends, so it wasn't horrible). I won't say there weren't times when I felt despair.
However, I just kept whacking away at it. I sent out hundreds of resumes, called dozens of places, cast a wider and wider net, and lowered my expectations again and again. Finally I got a job selling running shoes at a sporting goods store. The money was awful, but SOME money coming in is better than NO money coming in.
I kept applying for stuff I thought I wouldn't hate. I kept going to as many interviews as possible (working nights/weekends at the sporting goods store so I'd be free during the day for interviews). I got told more times than I can remember that I didn't have the experience/technical knowledge. I raged at myself for not getting an engineering degree or something in the hard sciences.
Finally, after about 5 months of concentrating searching, a really good gig just fell into my lap. They were desperate to fill a vacancy, I had two really good interviews where, being entirely honest, I just got lucky with having on-the-fly answers to their tricky little questions. I was hired into a job where the money is solid, the benefits are great, and the opportunities for growth are very good.
I'm not sure if I'll go to grad school for my PHD, (my ambitions are more in academia than making a lot of money) but whether I stay in this field for 5 years and pay off my undergraduate debt or stay in this field for 30 years and retire, it's work that I don't mind with people I like, and that's more than a lot of people can say.
A lot of people will tell you college is a waste of time unless you're a 4.0 double-engineering major with 14 internships, but I have to disagree. Yes, technically, I could have purchased all of my textbooks and read them by myself without paying hefty tuition. On the other hand, even though I didn't work as hard as I should have during my undergraduate years, I say that it was definitely worth it. The experience of college was really vital to my growth as a human being, even though I don't have a vast array of hard technical knowledge at my disposal.
Anyway, college is worth it/nuh uh isn't really the subject at hand. I'll just say that as a recent grad who was far from a model hire, but has found good, gainful employment, keep on keepin' on. Grind out the applications. Trawl the employment sites like monster. Look up labs where you might like to work and call 'em up. See if any local colleges or universities need a guy to answer phones in the admissions department or something- oftentimes at higher ed places, even if the pay isn't great, they'll let you take a class or two for free. It'll keep you in "school mode" and make up for the fact that a lot of administrative positions at a college aren't very intellectually challenging.
Another thing to consider is calling up a few temp agencies if you're in a large city. I was striking out bigtime even applying to 25 hr/wk jobs answering phones. I set my resume to a reputable temp agency (and be careful, because there are a lot of bad ones in big cities, too) and within a month or so, I was getting called to work those 25-30hr/wk jobs for ~1.5 times my area's minimum wage. Would I want to do that forever? No, but if you could do that for six months while you keep searching for a job you really want, you'd at least have some money coming in. I know for me, the psychological effect of knowing "I've got work, I'm making a little bit of money, I can do this temporarily til I find something better" was HUGE.
I love running, but I HATED selling running shoes, especially since our clientele was mostly wealthy, rude, and stupid. But I knew at the end of the week, I would clear enough money to keep the search alive.
Keep your chin up, OP. If you keep grinding away, eventually, something will fall into your lap. It might take 1000 rejections before that happens. People in your situation close to you might say "wow, I can't believe you just stumbled bass-ackwards into that job, I can't find anything" even though they send out one resume a week instead of 50.
And remember- you don't have to work at whatever you find for 30 years. If you want to work for 2-3 years, maybe knock out some grad-school pre-reqs at night, then take the GREs and skedaddle, no one is going to hunt you down.