I Had This Lump In Anus That Seems To Come

i had this lump in anus that seems to come and go. when I have a bowel movement it seems to be there. but when I was cleaning my rectum during bathing it seems to be nowhere. I think it's there once when I was constipated. could it be haemoroid? it does not seems to go away. it's not painful. no bloody stool.