I agree, the problem is probably that you have porous hair. Although product build up is another problem that can cause your hair to dry out and stop responding to products. If you use silicones, heavy oils and hair cremes/butters while avoiding sulfate shampoos - it could be bad news for your hair. Here are some ideas:
1) Do a monthly ACV rinse. I use silicones often but shampoo rarely so this is my main line of defense against build up and dry flaky scalp.
2) Water is the basis of all moisture, if water isn't present - neither is moisture. For dry or porous hair you must be sure to seal on wash days. Sealing with oils and butters only locks in the moisture that's already present. (Or blocks out moisture if it is not already present.)
3) On wash days, seal in layers while your hair is still wet. Start with a creamy water based leave-in, follow up with an oil like coconut oil or EVOO. You can follow that up with a heavy cream or butter, but only if your hair needs it. You don't want limp, weighed down hair.
4) Instead of adding your daily moisture in the morning, try sealing at night. Mist a little water on the ends of your hair and rub oil on them. Cover with satin for sleeping.
5) If you have some free time at home, try baggying your hair for an hour when it starts to feel too dry. This always works as a quick fix for dry strands.
Hope this helps. For more info check out my blog www.Hollistics.com - It's all about growing healthy, beautiful, natural hair!