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I understand that you are worried about the movable lump that you can feel even after the bruise has subsided. However, in all probability there is no cause for concern.
Following a bump it is common for a bruise to develop with an underlying accumulation of blood which is called a 'hematoma' . In most cases the hematoma persists for a few more days after the bruising has subsided. Eventually the hematoma will be reabsorbed by your body without any treatment. So, do not worry.
In all probability there is no connection between your recent viral skin rash and this hematoma.
In case your hematoma is causing pain , you could apply heat over it for a few minutes in a day , that would help the hematoma get reabsorbed faster.
Hope this helps.
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