thank you for your query
you seem to have developed a seroma
or an abscess
under the incision.
in either case you need to start with antibiotics asap. and also show it your surgeon to get a check up done.if there is an abscess it needs to be drained and the incision area needs to be taken care of.
you can start with anti-biotics and anti-pyretics for now
also keep the area clean to prevent spreading of infection
wishing you good health