If the stiffness and aches started when you changed your pillows it is possible that it is related. The position of your neck on the new pillows could be causing stiffness in your neck and shoulders. It could however also be related to something completely different. Stiffness and aches can be due to increased levels of inflammation which could potentially be caused by a wide variety of reasons. It can be caused by stress, poor quality sleep, diet, poor gut health and more. If your symptoms persist it would be wise to make an appointment with a Functional Medicine doctor and be evaluated properly.