Namaste
From your history and doctors advice , it looks like floaters .. you are appreciating a small black Mosquitoe moving in direction of your eye movements.. Nothing to worry as it is insignificant issue .. it will not affect your vision or retina .. inside the eye there is gel like substance which liquifies in some part , which will casted as black spot to you .. continue the medication
Next Steps
If the black spot suddenly increases to 100s or 1000s , flash of light seen , drop in vision then visit ophthalmologist immediately
Health Tips
Routine yearly checkup will suffice .. neglect your issue , nothing to worry at all