Why are my citrus yellowing right now?

I am pretty sure that it is not because of the minerals in the soil.

I am guessing that the heat is drying the soil and not allowing the roots to ABSORB the proper amount of available nutrients from the soil.

Am I correct? I am also concerned that I might over water though.

Are you feeding it? If so how much and with what? Poke your finger in the soil before you water again. It does not need to stay extremely wet.