It can be a hematoma or infected cyst. Apply warm compresses and take some anti inflammatory drugs like Ibuprofen after consulting your doctor. If it persists then this blood may need to be drained.
It is very difficult to precisely confirm a diagnosis without examination and investigations and the answer is based on the medical information provided. For exact diagnosis, you are requested to consult your doctor. I sincerely hope that helps. Take care and please do keep me posted on how you are doing.