1 week ago I had a bloody stool, difficulty with bowel movements since. Minor pain left side of lower abdomen. Also, a vibrator was inserted in rectum during sex? How concerned should I be?

Very concerned. you could have a bowel perforation a simple tear or worse go to a gastroenterologist or the ER for an eval.
See a doctor. Without being able to exam it is difficult to answer. However you did have a object inserted and this can cause a tear at the anal sphincter. This causes pain when having a BM. The pain makes it so you do not have a full BM which causes constipation, causing lower abdominal pain. Please see a doctor for a detailed exam to make sure there is no other cause. .