Yeast infection ?

I’ve never had one before but I’m pretty sure I have a yeast infection due to itchiness and the amount of thick white discharge down there (srry tmi) I had unprotected sex exactly a week ago & woke up this morning with the infection. Could the yeast infection be from sex just now infecting me or could I have gotten it randomly and naturally ( I am on no meds, I don’t douche etc) also will just monistat or something resolve it ?