Lemon Tree Diagnosis?

IMG_9100IMG_9101Lemon tree diagnosis?

This is a meyer lemon, planted almost a year ago. It has never been happy. It’s planted in full sun but the soil is clay and gets quite boggy. We’ve had some cold/frosty mornings in Melbourne but it’s spring now and it still looks sad. It’s leaves have been curled and shrunken and yellow for months. I’ve fed it nitrogen, magnesium and a couple of broad spectrum fertilisers as well as good ol’ fashioned cow manure and I’m running out of ideas for how to make this little one happy. I gave my neighbours a Eureka lemon tree (a gift for our housewarming but two lemon trees would be excessive!) and theirs is growing really well. Would love some feedback on this one. Thanks!