Lemon trees usually have only one growth spurt in a year, usually in spring. Depending on your geographical location, this could occur early spring or late spring. Patience is required in the meantime.
Water retention in soil is a valuable trait. What is important for citrus trees, such as the lemon tree, is to ensure that the soil your citrus tree is growing in provides extremely good drainage. While their roots can exist in wet soil, they cannot survive in water logged soil and the plant will eventually perish.
Citrus trees feed from their drip line. This means that the tree's feeder roots will be in line with the outside edge of the tree's branches. Your tree is still very young so I'd not concern yourself too much with this, but it is an important consideration as the tree grows.
Back to the growth spurt...
As soon as you see the first signs of new growth, tiny leaf buds, apply liquid fertiliser and consider adding a "tonic" that might contain seaweed extract and/or soil micro-organisms in suspension.
Normally plants grown in compost might need lime (calcium carbonate) or dolomite (calcium magnesium carbonate) added to manage potential soil acidity, however citrus trees enjoy a slightly acid soil so this should not be an issue.