Doc saw small abnormality inside uterus during ultrasound. he said not to worry, it cud be from bleeding i have. follow up in 6 wks. what could it be?

Too vague...: "Small abnormality" isn't enough of a description to hazard a guess as to what your physician saw. I would recommend that you contact your doctor with your questions - ask for clarification as to what was seen and what the possible causes are. The one who did the test and has seen the US results is the best one to ask about the cause.