Seeing a black oblong dot that goes away like an afterimage (not a floater)

I had multiple eye exams but this was last month. It’s not a floater it’s like a black oblong shape that just appeared. It goes away and it’s always in the same spot sometimes i see almost like a blue smear of color too. I had 3 eye exams with retinal image and the doc looked into my eye with dilated pupils. This was last month as I said. I’ve been seeing this randomly and I have a tendency to panic so I don’t want to go back to the optho because I’ve been there 5 times in the past 6 months. I’m 19 and have no medical history other than myopia on the higher side from what I know