Hello there....There are many reasons for that...Do you have any history of injury
to the tooth?or is your tooth decayed? either of the causes' the infection spreads to the apical part of tooth and would result in sinus...that intermittently keeps discharging pus and blood...you have to either get you tooth root canal
treated or get it removed...
if you dont have any of the above mentioned causes' then the problem might be with your gums proper...Gingivitis
is the inflammation of your gums that happens because of accumulation of the deposits over your teeth....You need to get your scaling done...Following which a gum astringent
is prescribed that would take care of your bleeding gums
... Consult your dental surgeon for further clinical evaluation and management...