I would say "Edw kai ena xrono kai tesseris mhnes prospathw na se mishsw"/ "Εδώ και ένα χρόνο και τέσσερις μήνες προσπαθώ να σε μισήσω", there are other options depending on style. This, in Greek, implies the action is still continuing in the present time: "I am still trying to hate you etc." If the action belongs to the past it would be like "Epi ena xrono kai tesseris mhnes prospathousa na se mishsw/Επί ένα χρόνο και τέσσερις μήνες προσπαθούσα να σε μισήσω" or similar. (It is an interesting sentence. )
I am not sure which word you are talking about: Is it weather or human interaction?
Psíxra,(ψύχρα):Refers primarily to weather. Relatively cold weather. In this case you can say kryo, as jaiel says, it is similar but more generic.
Prixrá(ψυχρά): Refers to behaviour, tone etc. Coldly, in a cold, not affectionate manner. "He replied very coldly/ apanthse poly psixrá" In this case, I think "psixra" is the best word for "coldly", although there could be other options depending on context.