(the first photo is taken today, the other ones a year or two ago)

Please help! I know I'm not the curliest person out there, but my usually wavy hair has been falling very flat and won't hold on to any form whatsoever. I hate the many fly-away hairs, my bangs don't seem unified, they fade and spread out in a way I don't like. 

I used to have the kind of hair that if curled, kept their shape easily without any products needed. Now, no matter what way I shape my hair, they just fall flat after 30 min. 

My routine so far has been a simple one, I wash my hair with either some moisturising or volume shampoo (I often use Natura Siberica) and use the same brand's conditioner right after. Sometimes I use some strengthening hair oils (like Gliss kur oil nutritive), that I've gotten as gifts and for a summery texture, I sometimes use a salt water spray (Löwengrip). I shampoo once a week (sometimes less) and wash/rinse with water every or every other day. I don't use heat and I scrunch my hair with a regular towel and let air dry. I have very dry hair and most hair masks/conditioners only make my hair heavy and flat, not moisturized. I live in a cold climate so my hair is filled with static from October to March.

I've not got a specific brand or any "fancy" hair care products, bc up until now, I've liked my hair the way it was. I've had more work related stress recently and haven't been able to sleep as much as needed for the past year. My shower water is very rough and filled with limescale. I'm looking into those filtered shower heads. The water in the entire apartment building is pretty peepeepoopoo, so that's a somewhat unchangeable factor in this equation. I also started regular ADHD medication.

I'm hoping someone can share a light and help me out of my darkness. My dad's got thicker curlier hair and mom has fair, but wavy hair. Mine is something in-between, but it's been feeling really thin lately. 

TLDR: My hair has been feeling flat and thin. My hair routine hasn't changed in years, but I've been more stressed and gotten less sleep this year. My shower water is filled with limescale. I would love my hair to be thicker and wavier. 

Thank you! 

Hair falls flat :c