What Causes Sinus Pressure And Muscle Ache Around The Breasts?

Hi, I had a lumpectomy followed by 5 weeks of radiotherapy, completrd Dec 2015. Since the start of the radiotherapy I had dizziness and pressure in my head and sinuses, it got progressively worse over the course of the treatment and 1.5 years later I still have the sinus pressure but the dizziness has lifted. I have had a clear mri scan and attended an ENT but no one has been able to help me, I do not respond to any sinus medication or painkillers. Also I have muscle pain from the side of the treated breast,up my back on that side, up my neck, trigger point therapy has helped with this. Any ideas on the cause and treatment of the sinus/head pressure would be greatly appreciated.