I Have Some Upper Back Pain On The Right Side

I have some upper back pain on the right side that tends to subsidize as I lie down. My friend tried massaging my back in this region, and she told me that the area felt tense. Prior to this pain, I do lie down on my tummy a lot with my elbows propped up and scooping my head into my shoulders, so I thought this chronic pain can be caused by the way I lie down/sit etc. I also feel that the pain has caused my right breast to feel a little sore. A lot of websites are saying it could either be breast cancer or a strained muscle. I do not see any changes in my breast, but I sometimes feel like it is sore. I do jump to conclusions, and have been labelled a hypochondriac by my family and friends so I'm not sure if I'm aggravating the pain/soreness by thinking too much into it. I spend a lot of my time searching up my symptoms and linking them to every possible disease out there. I have made an appointment with my GP this Thursday. I have had this for almost a week now, and I am getting a little worried. The pain is not getting worse overtime, but I can feel it if I sit in a weird position or if I slouch.