From the description that you have provided, it could probably be a sebaceous cyst. It's a benign cyst
beneath skin with a central pore or punctum and may discharge cheesy oily foul smelling liquid.
As the lesion is itchy and painful, seems like it has got inflammed and infected. To treat the same
Do warm water compresses over the lesion
Apply a antibiotic cream twice in a day
If its very tender, may take an antiinflammatory painkiller like Brufen
Hopefully the inflammation should subside with these measures.
I would advise you to consult your doctor and get it surgically removed once the inflammation settles.
Hope that solves your query. Take care.