advice please

Looking for some advice! My period is late by 8 nearly 9 days I've took 4 tests and all negative. I'm not stressed or anything else and my periods are always either on the day there due or a day before never ever late and especially not by 8/9 days. I wasn't trying for another baby as my wee one is only 5 months... I was sexually assaulted and I'm so scared that I could be pregnant but I keep getting the tests back negative x