If you are going to a gym, it's common to have such findings. Since most of us right handed its common to have right side muscles little bigger than left side. But since you have said the nipples are not at the same line You need to take an X ray of the spine to rule out scoliosis ( bending of spine )
Next Steps
Consult a doctor nearby as he can check the strengths of the muscles in either side and find whether they are weak. For cervical and thoracic pain you need physiotherapy