dear patient thank you for your question.
Let me just start off my saying that without a hands on examination of your lump it is next to impossible to tell you what exactly it might be.
However i will try my best to point you in the right direction.
Lipoma: The most common cause of solid lump it is quite possible that is a lipoma which has now become a
liposarcoma and thus is red painful and expanding. A
biopsy would confirm so
Cyst: A solid cyst filled with cheesy sebaceous material may have become infected
Swollen lymph node:
Swollen lymph nodes are often caused by something as simple as a cold or the flu. In rare cases, the cause is something more serious, such as HIV or cancer.
Malignant tumor: It’s possible that the lump under your skin is a
cancerous tumor. Fortunately, the chances of this being the case are quite slim for most individuals, especially considering all the other possible causes of this condition.
After having explained all the possibilities i feel it is either an
infected cyst or a liposarcoma. Hence please have it checked by your GP