Student or Learner
Call me then if you're coming.
Is the above sentence grammatically correct ?
I'm not a teacher...
I think the word "then" is unnecessary.
Call me if you're coming.
But, if you include it - then I think you probably need a comma. (To be perfectly honest, I'm not sure about that ... but, if I were writing it with the 'then' in it, I'd write it this way.)
Call me then, if you are coming.
Presumabely, in this case, the 'then' means to call me at some future, appointed time - to let me know if you are coming, or not.