There are lymph nodes located in this area. Are you ONLY feeling the lump on the one side and not the other? It sounds like 2-3 cm can mean that it is slightly enlarged IF it is indeed a lymph node. Have you happened to have any allergies/sickness recently? This can cause lymph nodes to become swollen and harder.
I have the same thing, it is a tumor on my parotid gland (not a cyst). I have had it for over 12 years. The ENT always wants to remove it because, although mine aspirates begnign, they can become cancerous. I would check with an ENT to see if this is what you also have.