Terrible 17 months?

I always thought the "Terrible Two's" were the terrible time but no one said anything about it coming way before then. I notice everyday that Parker gets angrier and angrier when things don't go her way! She throws huge tantrums, screams at the top of her lungs and pretends like she doesn't hear Jeff or myself when we tell her NO! I know that she understands what no means and the certain things that are off-limits but it is like we are on mute to her! I love that kid but she frustrates me to no end!! Hopefully we are getting over our bad attitude early and then the two's and beyond will be glorious! Wishful thinking!