Missed period after 4 months?

Hey mamas. I just had my second 4 months ago and I've had 2-3 periods since my PP bleeding stopped completely around 8-9 weeks. 
But for the month of October, I completely missed my period! I'm 9 days late now. I have had all of the PMS symptoms.. acne, bloating, cravings, hormonal, cramping... yet no period. I also had a negative pregnancy test (we only had sex a couple times and used condoms). 
Has this happened to anyone else? TIA!