I need some seriouse hair help?

Now ive never been obsessed with my looks, I though I naturally looked good. When I went on vacation for a month and I have i left my flat iron at home and let my curly hair be free thinking this would restore it a little and make it healthier. Now it was but now that I got a new haircut where I tease it (scene hair) it looks good when its straight. But every time I do straighten, its not shiny and the tips always curl up and it didn't used to do that. I blow dry my hair dry, and than straighten it, I sleep on it and fix it up in the morning but its dull and not shiny. I wash it with cold water and only put shampoo at the top of my hair and let the shampoo work its way down. Can anyone give me a natural way to make it shiner and more manageable? Im about to buy the dangerously straight line from Herbal Essences but im unsure if maybe Pantene is better? Please help with all my problems, thank you so much! (: