We have 3 kids…5, 3, and 1 (girl, girl, boy). Our 5 year old, the oldest, has been BY FAR the most hard headed, stubborn, and emotive of the 3. Sucks because we are learning how to handle the new life stages as we go with her, and she is our biggest challenge in terms of temperament. She was throwing full on kicking and screaming tantrums waaaaay before any of our friends with kids the same age were experiencing problematic behavior from their kids.
As she approached toddlerhood, my wife wanted to try the modern positive/gentle style of parenting that is in vogue in some circles these days. Total disaster, and we changed course before long. Nowadays I would say our parenting style is to set firm but reasonable behavioral boundaries, and be swift with discipline when our kids stray outside those boundaries, but generally shower them with with affection otherwise. As our oldest became an older 4, now a young 5, despite some difficulty regulating her emotions at times (she is just such an emotional kid), she seems to know her parents love her unconditionally but expect her to act right based on the standards we have set for her. As a 5 year old she finally seems to have the ability to process the corrections she receives from us and apply them most of the time. The last ~6 months have been the most enjoyable time I've had parenting her. This is after about 4.5 years of really rough (often miserable) experience parenting her.
In fact, just this evening I took her on a daddy/daughter date to a nice pizza place. She was well behaved and mature the entire time, I had a good talk with her about starting kindergarten, and my heart is full. All that to say…set a standard and keep to it. Stay consistent. Things will get better.