There can be several reasons for the dark bruises but painful ones do need exclusion of a vasculitis
(inflammation of blood vessels) like disorder.
Do you have fever (low grade), fatigue
(symptoms of a viral like infection), weight loss
, and then the painful bruises? If yes, definitely a vasculitis needs to be excluded.
Viral infections like dengue virus requires exclusion if you are in India at this time.
Otherwise, a CBC, LFT, C3 C4, ANCA, ANA (screen), renal profile definitely are mandatory tests at this point in time.
Please get in touch if you have any further queries.