Step 1:
Get the help of a qualified and trained individual. I would not post on the TMF telling everyone something was wrong with my car, but I didn't know what...and to please fix it. No one here (unless they are a Psychologist, Counselor, Psychiatrist) can tell you exactly what is going on with you. It could be off chemicals in the brain, it could be simply needing a constant listening ear for your problems, or it could be some other medical condition all together.
As a side note, when I'm experiencing intense down periods, these things have helped me:
• Finding ways to end the pity party, IE: reciting reasons to be thankful. I know it sounds harsh wording it that way, but I have it pretty damn good. At the most base level, I have food to eat, a decent apartment, and a job to support myself. Anything else in my life is a bonus want that was fulfilled. Studies have even shown that people who are mindful and grateful for all they do have experience greater happiness. Be thankful not only for the "things" in your life, but of moments you experience everyday. Waking up while still in a warm bed. Seeing a sunset. All little things - moments that are peaceful.
• If you're living in "Sacrifice Mode", figure out how to make that your driving positive. I remember us discussing this in the past and knowing your mother has needed a lot of your help. Rather than lament at this, take pride in knowing your sacrifice is stabilizing and improving her life. If you cannot change the situation, change your attitude on it. We all create our neat and tidy little mental prisons that don't actually exist at all. You're free to choose to do anything you want with your life. Truly! You are.
• Take care of yourself physically. No over or under eating. No under or over sleeping. Exercise, ESPECIALLY if you don't want to. You cannot possibly expect to be 100% on top of your mental game with an upset and ailing body. Take yoga, go for a walk, join a cheap gym, etc. Eat correctly! Fruits, vegetables, fresh meats and fish, etc. Cut out the junk food because it only makes you feel sluggish and bad about the eating decisions you just made. (Ben & Jerry's is not your friend in your time of need!)
• Find little paths that sideline your actual goal. You mention NEST...a LOT. I imagine not being fulfilled in this way has bothered you for quite some time and continues to become a heavier weight on your brain everyday. NEST is an amazing place to attend if the money and travel funds are there. If not? You find closer events to attend. You create your own and hope people show up (ie: munches). If you aren't finding events here on the forum that are doable, you find other venues such as fetlife. You may have a few mixed in kinks with your experience, but hey, who doesn't like to see/try something new? Where there is a will there is a way. You need to find your will because right now it's being smothered by sadness. Just know that NO circumstance is forever. Not going to NEST is not forever. If one path in the forest is blocked, well ya damn well take another!
• Remember that you are your own best advocate. There is no magic wand that will "fix" your life. It's not broken. There are circumstances making you unhappy. Isolate and work to change them. Do not expect this to be immediate. If you want something you better damn well go and get it. Excuses are a broken crutch. They carry you no where and they are only holding you back.
• Take "pills"! No I don't mean things like Prozac. If you study other types of healing, there are several medicines found in the herbal aisle of stores that are mood enhancers that can definitely help give you a boost in your down times. They are not personality changers, nor do they bring you down a weird zombie-like path. They are an excellent alternative for those who have poor insurance who are looking for some self-help.
• Get out of the house - NOW!! Do not sit home away from humanity feeling bad all day every day. It's very isolating and amplifies the sadness you feel. Sit for a while at a bookstore and pick up something to read. People watch at a coffee shop. If it's your bag, join a church for the company. Take a class at a community college. Sit at a park and enjoy the day and weather.
• Volunteer. Simply stated and simply done. Nothing puts your life into more of a perspective than seeing the worst lots people have been given in life. Soup kitchens, homeless shelters, elementary schools, libraries, animal shelters, old folks homes and MORE always need help! Sometimes the most precious thing you can give to others is your time. If you are too self-focused, you will be very unhappy. One MUST focus on others. You will be helping and feel very good about the deeds you are doing. Bonus: you will meet others and put yourself out there! New friendships are practically a guarantee.
I hope you find some help in what I've said. But above all? Seek the help of a professional. Seriously. Please do it.