The sitting position is a prolonged isometric contraction. All muscles enjoy a range of motion that they can find themselves in. All muscles can get long, and then contract and become short. When you are sitting you have a handful of muscles in a contracted state. When they stay in this state for too long, they can quickly fatigue causing muscle pains, or in some cases remain contracted limiting the movements some people can do after prolonged sitting.
There is no position so perfect that it won’t, in time, provoke pain. There are postures that will provoke this pain more quickly. You need to be mindful to not find your head in front of your shoulders. The neck muscles were not made to be weight bearing and cannot take the weight of your head.
In this day and age we cannot just recommend no sitting. While there are stand up desks, there are no stand up cars-yet. So what can you do? Periodic (set a 15 min timer on your watch) shifts in seat height, seat length, keyboard/mouse/ monitor position bring fresh muscles and a refreshing of position= it can be quite ameliorating. Just a small change can mean a difference for the muscle that isometrically contracted when you are sitting, and the more movement you can incorporate into your sitting will limit how tight your muscles will be.
For more in-depth advice suited just for you, make an appointment and have the doctor address your concerns.