I've started flossing fairly recently, been doing it just over a week now, but whenever I do floss, I end up with a toothache in one of my front lower teeth, which lasts for several hours and is very sensitive to bite with. Anyone have any idea why this might be happening? Could there be a cavity in the tooth or something that I'm aggravating by flossing?

One thing about flossing is the teeth get use to this and often the sensitivity goes away but you really need to see a dentist. There might be something wrong that can be fixed now before it gets out of hand.