What Causes Irritation In The Thin Vaginal Wall?

i am 58 and irritated my vagina about 2yrs ago and spotted. went to doc and did ultra sound and all looked good. he said he was sure it was due to my thin vaginal wall. no spotting since till i checked for a yeast infection and irritated the walls again. it stopped shortly after and haven't spotted since except once in a while after sex. called doc and since it stopped was not concerned.