Stress, anxiety, depression, etc. can affect hair health. Even if you start taking care of your hair now, it might take a while for your hair to improve. E.g. it took me around 2-3 years for my hair to start getting better, and it's still not as good as it used to be.

Vitamins may or may not help. What is your diet like? Foods containing Omega-3 fatty acids, e.g. fish and nuts like walnuts, are always a good bet. I've been taking Omega-3 supplements on and off for the last two years, and have consistently taken 2000-3000mg a day over the past six months. Eggs, spinach, berries, tomatoes, and protein are good for your hair too. In short, things that are good for your body will also help your hair. I've significantly cut back on processed sugars, white carbs, alcohol, etc. too.

What's your hair texture like? I try to air dry as much as I can. Also, I try not to comb my hair until its dry, because wet hair is very fragile and most prone to breakage. It's easier to detangle my hair when its wet, but I try to resist that temptation. Instead, I'll work in some de-frizzing agent (e.g. grapeseed oil, hair serum, etc) into the ends and finger comb my hair while its wet. Then I'll either air-dry or blow dry my hair, and only use a comb when it's nearly dry or almost completely dry.

Friction with pillows can also cause hair breakage. Satin pillows might help. I tie my hair into braids (not too tight, because that can hurt the hair follicle) to prevent it from getting tangled while I sleep.

When I wash my hair, I always use a conditioner. I try not to shampoo every day, e.g. once every two or three days works for me. There are days when I won't wash my hair (I'll tie it up into a bun while I shower). This has definitely reduced the amount of stress my hair goes through.

There are "hair, skin, nails" tablets on the market, but they never helped me. Multivitamins might help if you have a vitamin deficiency. Otherwise, a good diet, adequate rest, and exercise should do the trick.

Let me know if you have any questions.