What Causes Breast And Shoulder Spasms?

Hello, My name is Maria, 31 years old, female. My problem is: very strong spasms in front area between my shoulder and my breast. It all started about 6 weeks ago with spasms for a few hours, one week none and again the same. since then the area is hurting when i am in driving position with my hands on the steering wheel. I had X-Ray and MRI scans and came clear. I'm visiting an chiropractor 3 times a week for the last 3 weeks, but without any result.And today was the worse day ever, spasms for the las 8 hours, sometimes more frequent then other...like 1/20sec i haven't had spasms in the last 4 weeks, until today. I tryed ibuprofen, biofreeze gel, and cold ice to calm it down, but with not much luck. Please help me and tell me what to do. thank you