Why might my bruises not be healing?

On blood thinners? If you are on blood thinners, take a lot of Aspirin or Ibuprofen or advil (ibuprofen)... You may take longer for bruises to go away. Ask your family doctornif you can use natural products like arnica cremes or gels?
A number of reasons. As dr. Morrison said, there are certainly several medications that can increase your tendency to bruise and to make bruises last longer than normal. There are also a number of medical conditions that can do this too. If you aren't taking any meds that can affect bruising, or if you are taking meds that you want to see if you can change, you should see your doctor.