Hiya justwatching, welcome to MFK.
Did the "poops" show up at the same time as the flies? Can you get a look at one under a strong magnifier? If the poops are hollow cases and contain small worms with tiny legs toward the head end and little beady heads then you probably have a midge infestation, there are many species, some types ot the immature ones make casings like caddis fly larvae do but they are much smaller and the adults are a bit smaller than fruit flies. As annoying as they can be they are harmless. The young feed on detritus and bacteria, most of the adults don't eat at all, just breed then die. More frequent gravel cleanings will reduce their numbers but the best way to get rid of them is to use fish like guppys, ricefish,etc. that might be a problem with the oscar, weatherfish like dojo loachs will also gobble them down and are big enough not to be an oscar snack. I suggest more careful feeding and frequent siphoning off of any detritus to help control them.