A negative hysteroscopy covers you for at least six months, which you are just a whisker over and it is extremely unlikely to be anything sinister.
My money would be on vaginal atrophy given your genital tissues haven't seen estrogen for several months and it is likely that intercourse has resulted in some tearing and abrasions of the thin and fragile mucosa.
This is the commonest cause of postcoital bleeding in postmenopausal women.