i am a 24 year old female and I have had a strange bruise on my back for years over 7 years actually and it grows and shrinks with back pain , I live a very active lifestyle and it really slows me down but I just work around it but it is quite concerning I have been to a doctor and got blood work and it's not cancer related I have not gotten X-rays which I believe my doc should have done anyhow it goes up one side of my back and a spot right over my middle spine and if I'm feeling lower back pain I will look and see a bruise right over the lower part also