suspect you was doing the right thing by feeding it as it looks like it probably is nitrogen deficiency but think you are expecting to much, once a leaf turns yellow it will not come back green you may notice the newer growth at the top of the plant to be slightly darker green but the old leaves at the bottom of the plant at best will remain about the same or if you are still not feeding it enough may continue to yellow and may move up to the next set of leaves.
nute burn and yellow do not go together if you ever have a nuteburn problem it will not result in yellow leaves the first signs of nuteburn is usually brown or black at the edges of the leaf and in more severe cases the leaf will curl under and most of the leaf will turn brown or black there will be no yellowing stage.