Sorry to hear of your problem so I have been looking for some clues from the information you have given so far!
You say:
A few years ago I got a bare rooted apple treeNow I am assuming that it is most likely to be a 'dwarf' variety which I find need different treatment to what you would give to an old/ mature tree.
For example my trees are 'minarettes' which have been 'grafted' on stock to suit the modern urban garden.
You have also said that in its
the first year the tree had some blossom on it, and I got a few tiny apples growing on it.This is pretty much what I would expect from a young tree!
I feel I should have pruned it in the winterI have a gut feeling that at least some of your problems are rooted in this area!
But! If your tree is similar to mine then you don't prune in winter you prune around now, I usually prune around the last week in August and the first in September, in fact I was only looking at my trees this morning and was thinking it was about time I got the secateurs out!
I do this by pruning the 'water wood' as I call it i.e. this years growth.
These are usually seen as long spindly growths which need cutting back to the
'basal growth' which is a bunch of leaves at the base of the growth.
If you find it difficult to determine what is basal growth ( which can happen) cut the stems back to 6"-8" (15-20cms) from the branch they radiate from and this should work equally as well.
Here is a link on how I treat mine!
http://www.thegardenersalmanac.co.uk/Data/Apple/Apples.htm