It looks like that your lower tooth is infected. It can be because of decay. As you do not have any hot and cold
sensation, it means the tooth has become non vital and pus formation is there. The pea size lump is the abscess
which is formed on the tooth. For this you have to visit dentist
, who will do clinical examination and take x-ray and find out the extent of decay. This tooth will require Root Canal Treatment
. The abscess can only be drained out by Root Canal Treatment.