Hello,
From your symptoms it looks like a bruise. The blood under the skin which causes the discoloration of bruising should be totally reabsorbed by the body in three weeks or less.
If the bruise remains or more such bruises appear without any trauma then please get an evaluation done from a physician. Anemia and deficiency of vitamins C, K, B12, or folic acid are the common causes of easy bruisability. Try taking iron tablets and multivitamins for some days and see if the symptoms improve. If the symptoms do not improve, get yourself evaluated by a physician and look out for SLE, bone marrow disorders, liver diseases or leukemias. Anti-clotting (anti-coagulants) medication also can cause increased bruising.
I sincerely hope that helps. Take care and please do keep me posted on how you are doing.
My armpits are bruised but do not hurt, itch, or burn for about a week but today one of them started to hurt so I started to feel it and it has a bump under it but the other one does not hurt it just look bruised with no pain or itch