... at least in Hungarian, -ka, -ke are diminutive suffixes, while the -i ending, just like in English, is a sign of the pet form.
So if we suppose that your name is of Hungarian origin, it could come from Natália (
Natalia) or
Natasa (both are legit full names here) shortened to Nati, plus adding -ka for diminution.
But note that this is only a
possible origin, it could come from a different source as well...