I'm really getting desperate for some kind of relief.I really can't find anything concrete for help.

Thank you but this is in my brain,so I don't know how diet can help me 

Then follow healthy diet

This is a potentially serious condition.  It can cause cancer, worsening headaches, loss of coordination, brain damage, and sometimes death.  It’s cause is usually congenital or as a result of a head injury.
Like it or not, you must see a specialist doctor for proper diagnosis and treatment.  Depending upon the nature, benign or cancerous, the location, the size, and symptoms, it is treated in a large range of ways.  Small, benign, asymptomatic, cysts not growing or in a dangerous area may be simply monitored without treatment.  If cancerous or pre-cancerous, laparoscopic brain surgery is the preferred treatment , although open surgery may be required.  A large benign or growing benign cyst is either shrunken by no new surgical means or removed surgically.
Smaller congenital arachnoid cysts are often discovered by accident during scans for other conditions, ie, concussion, headaches, brain injury.  These will either be monitored or removed  during surgery for another condition.

The diet sounds like a good idea regardless of whatever your diagnosis and treatment.  Self-diagnosis of anything in the brain is unwise.  You must see a doctor, maybe a few for other opinions.  Get a proper specific diagnosis and from there choose with a doctor’s assistance, the best course of action.  

Of course, pray to the Mother of God, Mary.  She will guide you regarding this trial.  May you be returned quickly to health, if that is God’s Will.  God sends trials for our good.  I pray you will learn and grow spiritually through this trial and emerge a stronger Catholic, closer to the Sacred and Immaculate Hearts of Jesus and Mary.  

I have no experience with arachnoid cysts so I can't vouch for anything but so far this is the only non-surgical recommendation that I've found:

Natural Treatment
This would address treating symptoms such as headache or nausea.
- ACV, cayenne pepper and turmeric help many with headaches. Aroma therapy and massage, biofeedback, relaxation techniques, feverfew or rubbing on oils (lavender).
- Drink up to 8 glasses of water daily. Do not drink any caffeine.
- Put a cold, moist cloth where it hurts. Do not use a warm or hot cloth; it will make it worse.
- Nausea may be helped by charcoal, baking soda or sniffing alcohol swabs.

https://www.earthclinic.com/cures/arachnoid-cyst.html

I did have MR done 2 times.And I spoke with two neurologist.The last said to me,that I should go to the surgery,but later he told me that if he did have the cyst,he would not go to the surgery,because every operation is risky lol So if a neurologist would not have the operation,why would I go? I remember reading that for every sickness there is a herb for it.I wish I could find it...

It is true that every brain surgery has it's risks.  But also sometimes not treating a tumor or cyst can also have risks.

I have a friend who went blind in one eye from a benign tumor near her pituitary gland and eventually the tumor started growing and over the course of trying to find natural remedies the tumor started putting pressure on the other eye and she could have become completely blind with 5 young children. 

She had successful brain surgery recently and is able to relax about the tumor and not stress about it anymore and not being able to take care of her children.

earthclinic.com

Arachnoid cysts are located in the arachnoid space, which is not IN the brain but a membranous space surrounding or cushioning the brain and spinal column

Is the cyst(s), small, causing you symptoms? Does the doctor say it's obstructive in anyway ( blocking the flow of cerebral spinal fluid?) Is it so large that it displaces any (brain) tissue?

If it's small and not causing symptoms, I would just watch it ( they can get larger).
People live with these and many don't know they have them.

Larger ones causing problems should be drained/removed. Be confident that the surgery does not involve invading brain tissue.

So perfect! So refreshing to see a rational plan.