With no health insurance/money and a complaint about health, what do YOU think you can do to make things a bit better for yourself? Live healthy seems about the only option to me, and hope for the best, and try not to dwell on this because worrying ALWAYS makes these things worse (and never better, unless you can actually get some professional help in which case a little worry over things like this is healthy). So how do you 'live healthy'?
#1 in your case seems to be quit drugs, since you believe the problem is a direct result of drug use, and that further drug use has exasperated it. Whether drugs are truly to blame is irrelevant if you can't find this out for sure, and already have some belief that they are to blame. Includes Alcohol and Cigarettes obviously, Caffeine/Coffee always gives me a headache, but I do find having a cup or two of tea a day to be negligible on my health.
#2 is exercise, because this will promote a healthier body and brain, give you some pain relief (releases endorphins), and will also promote the next steps very well also. 15-30 minutes of cardio 3-5x a week and some push ups, sit ups and light free weights 2-4x a week is all that is needed to really reap most of the rewards exercise gives you. That's about 4-5 hours a week. Also STRETCH, or else you'll be in pain.
#3 is sleep, since your chief complaint is with your brain and sleep is when the brain can rest and heal the most. 6 hours minimum, 10 hours maximum, every night around the same time, at or before midnight is a great rule to follow, as this will ensure you are awake when it is light out, the sun and seeing it often is good for your mental and physical health (vitamin D!).
#4 eat healthy, as this will provide you as much protein, vitamins and nutrients that your brain needs to heal itself. Focus on fruits (especially high in anti-oxidants), vegetables, and meats. If you don't think you're getting enough of any of these, then replace your chips with an orange or banana, fries with a salad, and simply eat something high in protein at least once or twice a day. That reminds me that eating every meal is incredibly important and even better is just eating healthy snacks 6x a day.
I ain't saying this will heal your brain, but its the best chance you have and if anything you will feel incredibly better in every other way at least in a few weeks to months following these fairly easy to follow rules.
EDIT
After reading your post before this, it does sound like something I often experience and I think most people do, and generally don't worry too much about. Look up tension headaches. Also, watch your posture and how much stress you are under in your life. Tension headaches could be causing your sinus/back of eyes pain and poor posture could lead to a sore neck/lower back of the head.