Joanne I wish I could tell you what causes it but we do not know--there are theories but we have no clear cut answer--they are more common on the lower but that doesn't help your discomfort.
No, I do not smoke, drink or eat any sweets - yes I am quite boring really!! The one root socket (if you know what I mean!)did not bleed in the first place. There were three roots on this molar, two were fine and the root along side the root of my mouth did not.
Are you smoking, drinking through a straw ,or sucking on hard handy? This can attribute to dry sockets. Something is moving the blood clot out of place.