I see negative afterimages often, have light sensitivity, quite a lot of floaters and when i look at a wall or any object for that matter which is plain, i see a flickering effect (though there is no real flicker). retina is normal as per doctor?

If you saw an ophthalmologist he/she should be able to tell you what is causing these symptoms if not the retina. If not satisfied se another reputable one.

Among the things that you didn't mention were whether this was occuring in both eyes and whether this was new. This could range from something serious like inflammation (uveitis) or retinal tears/detachment to something trivial or nothing at all. You should have the doctor who examined you give you a better idea of what this is and isn't.