I have had a circular purple bruise with a white center for about a week. there is what feels like a knot in the center. pain is just relative bruise ?

Check closely for ch: The hard central part concerns me. You need to assess its size and then watch it for 1-2 more weeks to see if the hard part is getting bigger or smaller. If it is growing in size you should go see your doctor. A biopsy may be required for further assess the cause(sometimes tumor can present with a bleeding around it , resulting in a bruise.

Bruise: Without details, it is hard to interpret. Where is/was the bruise? Did it occur spontaneously or was it the site of trauma? The white center suggests either an immune reaction or an inflammatory pustule. Were you taking any medications at the time? Did this ever occur before? Please respond with answers to these questions.