It may represent a haematoma
, ie an internal bruise due to bleeding of the tissues, underneath your skin. It is quite common to have such a haematoma for many weeks, and in some cases, many months before it resolves fully.
Be aware that, there is a chance this haematoma can become infected, ie cellulitis
, which is infection of the soft tissue
. If the redness
does not resolve or gets worse, it is best to be seen by a doctor to exclude this possibility.
It is not a 'blood clot' as I think you mean ie a thrombosis
which is a clot in the veins. It is a type of clotting of the blood in the soft tissue, ie a haematoma.