Talk to General Physician on Severe Back Neck Pain

My age is 23, and currently working in IT industry as Machine Learning Engineer, where i have to use laptop screen for 8,9 hours. I have severe back neck pain, I think it is due to my sitting posture while using laptop, or due to double pillow while sleeping, Pease tell me how i can reduce this pain. How can i improve my sitting posture on chair while all the time typing something (so arms are bend at a constant angle) I don't know either I'm guessing or not, but i tried to give you my history of back neck.