This symptom can be attributed to a swelling of the lymph nodes, infections or cysts.
In first term, take into account that the lymph nodes perform as filters that trap microorganisms or cancer tumor cells. When they do so, their size increases and are easy to feel and their swelling generally stops in few days.
The subcutaneous cysts or abscesses, in the other hand, can also result in big and painful protuberances caused by shaving or the use of antiperspirants. This is something common, especially in teenagers when they start shaving. Some other causes include adipose tumors (inoffensive adipose tumors) and the use of certain drugs or vaccines.
It is important, explains the portal Medlineplus, not trying yourself to diagnose your protuberance, and this is why we recommend to visit a specialist if the protuberance persists for more than three weeks. Your doctor will ask you, for example: when did you notice it for the first time? Has it changed in size? Is there any situation that worsen the problem? Is it painful? Or, do you have any other signal of alarm? The specialist will probably request some other tests for being able to produce a more complete assessment.
Related: Diagnosing swollen lymph nodes