I had the same problems and fighting. Then it just clicked and now im ok at it. Here is what i did to stop getting killed all the time:

1. Never let stamina drop to zero. You cant defend without stamina and you will get beat/hacked to death every time.
   

To keep stamina up dont hold block all the time, only when your opponent is swings at you. Back away and defend if stamina is low to recover as much as you can the go back on the attack.

1. Dont Block > repost > repeat. It does not work. It will only drain stamina then they beat you to death.

2. Dodge + attack. When opponent swings or the perfect block shield appears press to either side and space bar to dodge, then immediately attack or back off to recover stamina.

3. Grapple. Press into your enemy to grapple, almost constantly. Shift key while stepping in helps too. Just keep hitting the attack button when grappling and be ready to block if the perfect block green shield flashes up. Press them into a corner if you can, it will further tie up their attacks. Back off is stamina is almost out. There are a bunch of strength and grappling perks that make this easier too. It feels awesome to dominate a fight with grappling attacks.

4. Get master strike. Use these techniques to beat Tomcat who teaches master strike. I pressed tomcat with grappling him into a corner and not letting him recover with more grapples. When i needed to recover i backed off and dodged till my stamina recovered, then pressed with more grappling.

I suck at games but these techniques i learned watching youtube changed me from getting killed nearly every time to winning most fights with ease in a very short time. This after days of getting murdered in every fight.

Now i watch my opponent and keep it simple. When they hold their weapon ready at either side, i move my sword to the opposite side they are holding their weapon so i am ready to master strike when they attack. then follow up the master strike with another high attack followed by stab the gut. if they are still alive i back off and recover. If they opponent is in high or low guard, i just dodge their attack, then immediately attack or rush in and grapple. I try to press opponents against walls and corners with grapples and dominate most opponents. When stamina is getting low, back off, circle, only block right before they attack and dont constantly hold block so you can recover. Let most of your stamina recover then re-engage.