Hello,
You should have mentioned your age. Lumps under the chin can arise from the skin,
salivary gland, Lymph node.
Just below the skin the common swelling is - infected
sebaceous gland - called as a sebaceous cyst
The salivary gland (sub mandibular salivary gland) may get enlarged due to the block of its duct
The commonest is enlarged lymphatic gland - due to infection anywhere of its drainage area
All the above three lumps are soft to firm in consistency and moves horizontally and vertically.
Pain indicates inflammatory swelling
You say you noticed only yesterday and you had
cold sore 3 days ago and
sneezing - so possibility of infection is more. Watch for infection in your mouth, cheek, palate, tongue, teeth, throat and lower half of your face.
The “BEAN” size goes in favor of initial stage of sebaceous cyst or lymph node
The points against your swelling are the Hardness in consistency and not able to move.
Drs only can assess the hardness and motility.
Better to get an opinion from an ENT surgeon and if necessary a
General Surgeon.
Confirm clinically what may be the provisional diagnosis of that swelling and treat accordingly.
My best wishes