Pus is a product of local infection, may be you have not kept your hand clean after an open injury
Are you able to flex your finger?
Is pain a pricking type of pain?
If you are able to flex your finger and pain is pricking type, it is probably due to infection and needs antibiotics.
But the history is not clear and complete, if possible visit a local doctor or contact me on Private chat.
Next Steps
Needs further management, but lacks complete history.
Visit a local clinic or get back to me on private chat.