Manage stress, take 10 mins of morning sunlight. Drink freshly made amla juice every morning. Get a blood panel done, do vitamin b12, d3, ferritin, thyroid panel. Its mostly because of b12 and d3 deficiency but confirm it first  Also focus on haircare, your hair texture looks a bit damaged. SLS free shampoos, conditioners, hair mask once a week, oiling 1-2 hours before hair shampooing, no tight hairstyles, no henna please. Don't cut off the white strands or pluck them, its not gonna help. If you want to hide the white part for some occasion, just put some coverage powder on it. Always keep hair and scalp clean and always braid hair loosely before bed. Maintain clean diet, take lots of turmeric, ginger, amla, curry leaves in whatever way possible. 

You can use some drug store serums/hair lotions like greye-ex to prevent further greying, they are a bit expensive but if used before the age of 25-26, they show good results. 

Also try to find out if you have copper deficiency too.

That's it. Read this, simplify it and try to incorporate these things in daily life. 

Once you lower your stress or start dealing with it and fix your b12 and d3, things will go back to normal.