Hello - as I have several Citrontrees and they look very different from yours, I must say, that it seems to me, that there are several different problems.
The pot seems to be tooooo little. The pot seems to be out of Stone. The earth is not enough for the roots, and the roots are turning around in circles at the wall of that stonepot, which is worst. The Stone is cold, But the roots love it warm.
So first put the Tree in a 40 cm plastic pot, use normal plowerpotsoil, give bio fertilizer ( f.e, dogshit in the earth), water the plant with rainwater; put water together with a little bit vinegar in a iron can and when the water is really brown you can water the citron with it. The Colour of the leaver will turn into a dark green and they will be flat and not rolled . Then you can expect a nice harvest of lemon fruits.