Lump in this area of the foot maybe due to a soft tissue infection
, if it accumulates pus unddrneath the skin it will increase in size and gives more pain. It can also be an infected insect bite or scratch wound if you remember having bitten or scratched in this area. Pain reliever can help but it would need an antibiotic if it is due to a bacterial infection. See a doctor if pain reliever does little help or if you suspect an infection so that an antibiotic be started.