Rastagirl, I know you recently transplanted but you need to again, and soon.
I'd suggest a 8 liter container.
And if I were you I'd seek out potting soil that was rich in organic nutrients such as:
worm castings
bird & bat shit
seaweed/kelp.
It's better to use organic soil already rich in organic nutrients than to add them. You'll still have to add nutrients, but less than before.
I betcha that if you switch to a bigger container and spend the extra $$ for top of the line potting soil, as soon as the roots hit that new soil you'll see explosive, lush growth.
When you do transplant, water just before & after with horticultural vitamin B-1. You can purchase it alone or use a product that already contains it (in the states example Thrive Alive).