It looks a whole lot like a severe nutritional deficiency: just like eggplants citrus trees are very heavy feeders and require a lot of fertilizer to grow properly.
There are several citrus-specific agri-grade liquid fertilizers you can use right now: they are much cheaper than standard liquid fertilizers and can be applied either by watering or spraying the leaves. You can start using that right now and then apply some slow release fertilizer over the cool season.
