Hi, actually the condition you are referring to is also called as granuloma, since it is a soft tissue lesion it is not visible in x-ray. It occurs due to any kind of allergic reaction, hormonal imbalance and several other causes. The treatment is to visit a periodontist and get it excised (removed) and sent for biopsy to know the underlying cause otherwise it can occur again.
take care

HELLO AND WELCOME,
the bump may be due to accumulation of plaque and food debris b/w the teeth.
there may be bone loss and periodontal pocket too.periodontal destruction and gingivitis cause bleeding gums.
visit a dentist and get deep scaling and root planning done.
get an x-ray and if there is severe bone loss,bone grafting has to be done.
if tooth is mobile ,inter dental wiring/splinting has to be done.
use soft-interdental brush and dental floss to clean interdental areas.
use chlorhexidine mouthwash to prevent accumulation of bacterial flora.
clean your mouth after every meals.brush your teeth twice daily.
take tab.doxycycline-100 mg,once daily for 7 days to make gingiva intact,firm and resilient.
regards
DR.BINDIYA.

Hi,
dark red bump between 1st & 2nd molar which bleeds after brushing is more likely a Granuloma.
As dentist couldn't find any pathology in x-ray which is taken three times then involvement of periodontium is not the issue.
Yes, Granuloma has to be treated by excision & that excisional biopsy should be sent for examination.
Unless it excised, avoid forceful brushing as granuloma tend to bleed even on slight touch. Severity of bleed depends on the size & condition of granuloma.
Also get your teeth cleaned by dentist (scaling) to avoid secondary infections.

Take care.

it is probably due to pocket formation in between the two teeth. your dentist might be missing bone loss between the two teeth which is a very important sign .please recheck the xrays before going for biopsy .