Haircare tips please ?

Hiii... Lately my hair quality's descended.. I wonder why ! Recently got a new job that involves sitting in an Air-conditioned room and working on laptop all day long. My hair sees no sun. It has become very dry and rough. Humid temperature of my city spoils it even more whenever I am not at work. Hair is extremely dry after wash and starts becoming oily later in following 2 days. Head massage with warm coconut/almond oil gives me oily dandruff. Hair looks dull and has almost stopped growing below shoulder length. Suggest me a way out please ! I have never done any hair coloring or do not subject it to straightning or curling usually. Suggest me if I need to follow a certain diet plan. Anything I can do to fix this and grow my hair long over 5-6 months please suggest me? Also what can I do to improve volume ? Thanks in advance !