My kitten is growing up and NOW starts figting with older cat?

i got a female kitten (not spayed) in ... i dunno, like beginning of may. she was eight weeks old, so now she's like 3.5 months old. she's cuddly but kinda crazy. My other cat's (female, spayed) a year old and she's cuddly and nice, and at first when she met the kitten she hissed at her, but then they started to get along, and then they were friends and would cuddle. But lately, whenever they see eachother they fight and yowl and run around the house yowling and attacking eachother. why are they fighting and willt they ever stop??? no stupid answers plz