A report by a 2005 International Agency for Research on Cancer (IARC) working group said COCs increase the risk of cancers of the breast (among current and recent users),  cervix and liver (among populations at low risk of hepatitis B virus infection).  A 2013 meta-analysis concluded that every use of birth control pills is associated with a modest increase in the risk of breast cancer (relative risk ) and a reduced risk of colorectal cancer (relative risk ) and endometrial cancer (relative risk ). Cervical cancer risk in those infected with human papilloma virus is increased.  A similar small increase in breast cancer risk was seen in other meta analyses.  
Two possibilities to mention:
1. If your skin is tender to touch and burning is not affected by body movements and different positions, then it can be shingles (Herpes zoster virus reactivation in one of the spinal nerves). Nausea can be also from shingles. This causes burning pain going like a stripe from the spine to the front. Often (but not always) rash appears after some time. Neurologist would tell you, if there is any available painkiler for your situation.
2. Bulging or herniated disc or some other disorder in your thoracic spine (osteoporosis, arthritis..) could cause pinched spinal nerve. This type of pain would be affected by different body positions and would not be tender to the slight touch. Again, neurologist could say more.