Hi Susan,
I've put quite a bit of thought into possible ways to help alleviate the pain you're having. First of all, when muscles are constantly tight it is a sign that they have been strained and are close to being over extended. Muscles tighten in order to protect themselves from being pulled to the point of injury.
The first instinct in dealing with tight muscles is to try and stretch them out to relieve the pain, however it is rest that these muscles need, not more lenghtening. Rather than stretching the muscles of your neck and shoulder, try opening the muscles of the chest in order to take the burden off the tight muscles. A gentle way to do this is to lay on the floor with a rolled up blanket or a bolster under the upper back. Place a block or a rolled towel under the neck and then get as comfortable as you can. Relax into this supported chest opener and stay awhile.
I would suggest working with chest opening postures and being aware of the alignment of your spine, especially the cervical spine. Keep your neck long in all your postures and work to prevent dropping your head forward or back. Dropping the head back places an undue amount of strain on the muscles of the neck and shoulders and in most cases is unnecessary in the majority of postures. Only in an advanced practice should one even consider dropping the head back in postures such as Upward Facing Dog because of the amount of strength needed in the neck muscles to keep the cervical spine from being compressed.
I would also recommend seeing an Injury/Sports specialist or a physical therapist. They can help you identify what is happening in your posture that is contributing to the chronic tightness and can certainly work with you to develop a physical regimen to help release the muscles.
Be aware that your muscular system will work to compensate for the tight muscles in your neck and shoulder. This can lead to other problems concerning your posture and the other muscles that work to compensate for the lack of range of motion.
Best of luck Susan. Please let me know how it goes!