Some points to address:
1. Get armor. Any armor. Gather even simple cloth, duct tape and make padded armor, which doesn't slow you down, but gives decent protection. Having it on where you can you'll feel the difference, I certainly do.
2. Wait for the initial swing of a zombie. They usually start swinging as you come closer for the first time and when they miss it's some time before they can attack again. There's your chance to land a successful hit on the head and if it staggers, you've can hit again before taking a few steps back.
3. If a zombie gets enraged, start slowly backpedaling. If its speed is greater than you anticipated (starts gaining on you), quickly turn around and run off a few meters. In most cases they won't be able to catch you when you're running and the distance it has to take to catch you will more often than not make it stop enraging.
4. If you feel uncomfortable with hitting multiple times, relying on Zs not enraging, focus on doing single power attacks. Good aim is needed using point #2 to attack after they did they swing. Back off a few steps and if they get enraged after you hit them, you got enough space to run a few more meters for them to stop being enraged.
5. The lowest difficulty makes zombies not only easier, but also has very low chance (if any at all) for Zs to get enraged.
6. Try different weapons. Knives have short reach, but give bleeding debuff. Clubs are okay, but heard spears have very good reach and attack fast.
Most of this is trial and error. If you spend enough time, surely you'll manage to get a good grip on something and move forward from that.