First of all, I've been having the same problem (although I'm 36), so I empathize. I agree that stress & depression are the most likely causes, but knowing that doesn't really help you, does it?
I suggest seeing your doctor to rule out other causes. Lots of different things can cause low libido. Usually it's something "minor" like stress and/or depression, but it can also be a sympton of more serious illnesses (e.g., cancer, HIV infection) so take it seriously and get it checked out.
In my case, my doctor tested my testosterone levels and my brain hormone levels (because, as I understand it, brain hormones regulate testosterone). If the brain hormone are off, that can be a sign of something serious (e.g., a brain tumor), and then I would have begun treatment for that. Fortunately, my results were normal.
I don't mean to freak you out. It's unlikely that there's any physical illness, but there's no harm in getting it checked out. Most likely your problem is "just" stress and depression, so once you've ruled other things out, you can start dealing it. Your doctor may recommend counseling. If you can't afford a psychologist and don't have health insurance, ask your doctor if there are free mental health services in your area, or maybe try talking to a social worker.
Do whatever you can to try to improve your life. If you can get back into school, that's great. If you can't, then explore other options. See if there are any job training programs that might work for you.
Also, when you're not trying to deal with the work/school aspect of your life, try to spend more time doing things you enjoy. For example, f you like playing cards but don't do it very often, try to set up a regular game. If you play an instrument but don't get to play much, try to make time to play more often. Or maybe it's time to try new things. If you like sports see if there's an adult softball team, or volleyball, or even dodgeball (like the movie). Your community probably had adult classes that are just for fun, not career-oriented (like art, photography, cooking, dance, yoga/pilates, astronomy, etc.)
Those may sound like horrible ideas to you, but they are just suggestions. The point is to find some things you like doing because doing them will help you stay mentally, creatively, and socially active. Try not to worry about sex and dwell on your problems. If you are able to start enjoying life again, the depression may lift, and you may find your libido coming back.
Best of luck to you.
