It is normal for a young tree to drop excess fruit it cant carry, you'll only want it to develop a few oranges (if any) the first few years anyway to build the strength of the tree. Its spring so its not unheard of for leaves to be slightly yellow now, you've done a good job at keeping the grass back from the base of the tree but the surrounding grass still might be stealing some of the fertilizer your putting down and you may need to use a bit extra at your next feeding. But I don't have oranges and am not positive if they are much different in fertilizing requirements than Lemons & limes. If your worried about over-watering, dig down a few inches in the soil and see if its wet. if its really wet hold ff another day or two, you may find the surface is wet but deeper down is dry too so give it a good checking out I know in ground trees can take more moisture than container so it shouldn't need to be dry. I use copper spray for my Peach but I haven't on my citrus. Its best to not to treat if your "shooting in the dark" it may stress the tree out more. Its young and its a transitional season it may just need some time to bounce back from putting energy into making flowers and fruit. Hopefully someone else will chime in if they see anything else that you could be doing to have it improve. Good Luck!