Come on the Lemon Tree!

Optimistic as ever I like to think that my lemon tree will be ok, despite the fact that it has about five leaves left and is looking a bit sad.  I must say that a move into a sunnier spot seems to have done it good.  In my search for answers I joined a gardening forum and "asked an expert".  This is what my expert thinks:

I am sorry to see that your lemon tree is doing so poorly.  There is no reason why your lemon tree shouldn't do well.
Firstly, citrus trees need to be planted in a full sun, protected from cold winds position.  They need a well drained position and need regular feeding during the spring/summer months.(Dynamic Lifter for Fruit & Citrus).  From what you have said, your tree appeared to do well during the warmer months.  Look at the position it is planted in and if necessary, move it to a more suitable spot.
It has been a particularly cold and wet winter this year and perhaps this may be the reason why it leaves have turned yellow and stated to fall off. Check the potting mix you have planted it in and make sure the drainage holes in the bottom of the tub are not blocked.  If the roots are too wet and waterlogged, there will be a lack of oxygen available to the root system and the plant will consequently suffer.  I am sure if you relocate the pot to a full sun position, check that the potting mix is well drained, you will notice it will start to pick up as the warm weather approaches.

The expert seems positive so I feel positive.  Come on lemon tree!