Neck isometric exercise, trapezius stretching, Ultrasound therapy continuous mode for 7 mins, tens for moderate pain for 15 mins need to be used...

Chiropractic adjustment will help. Take frequent Breaks at work. Core Strengthening Exercises. Use cervical pillow.

Both will work to reduce

U can go with both us  and tens

Both modalities have their own role ultrasonic works  best on tightness and tens works best on pain. A combination of both along with hot fomentation gives best results and instant relief.But exercises are a permanent cure for muscular problems.

Cold fermentation followed by heat treatment to neck and shoulder region for larger area then ultrasound treatment for stiff  area .TENS in add on can be beneficial depending on  your constitution

Take IFT or TENS along with ultrasound they always work in combination , anyone will not help .

U need to be applied Hot Pack or Hot water fomentation firstly for 15 minutes at least. Next to that Ultrasonic should be applied for 7 minutes. And next to that Tens should be applied for 12 minutes. Prescribed exercises should be started from 4th day of starting Physiotherapy Treatment which will be the permanent cure. Keep using pilow of medium thickness.This all for 7--10 days.Take Physiotherapy twice daily for 1st four days for faster relief.

Combo of Ultrasound and TENS will be more effective for you, followed by HWF. Your pain will be go by both,but for permanent relief you need to some prescribed exercises.

Your problem become chronic now tens and ultrasounds both work temporarily. So visit some physiotherapy setup and reassess your problem.