So there's a couple things it could be, but the most likely answer is simply: inexperienced player vs experienced player. Remember that Below 50 doesn't actually mean everyone is new. That campaign attracts a lot of veteran players who enjoy below 50 PVP. If you can, its a great idea to learn from the veterans on your own alliance, group with others, or join a friendly PVP guild.

Ultimately, the answer is practice. We all got better with practice. We also all died a lot getting that practice, so you aren't alone!

Tanky/Defense
1. Impenetrable trait gear that is close to your level. If you dont have impen, you'll want that crit resistance. Below level 50, you benefit from Battleleveling, which scales from your gear level and quality. This is why you might see a level 10 in gold quality armor absolutely wrecking people. On the other hand, if you've outleveled your armor, I find that I become squishy AF when I'm five or so levels above my armor level. Yes, replacing armor is a pain, so it might be worth finding a decent crafted set you like and see if someone can craft it for you. Finally, a lot of PVP builds use Heavy Armor for greater defense, but its up to you if that's a worthwhile tradeoff for you.
2. Heal and Buff proactively. Heals over Time do a lot to blunt burst damage and keep you out of execute range. Its a lot harder to recover in PVP - its easier to just not get to low health in the first place. If the enemy gives you breathing room or you can gain breathing room with cloak or using line of sight, use that space to heal and recover your resources for round 2.
3. Reflexes - these come with practice, but it helps a lot to blunt a sudden attack if you learn to block, dodge roll, and hit your HOT, or whatever the defensive combo of your choice is.
4. Situational awareness - this totally comes with practice, but as you continue to fight you'll learn more about the mistakes you made and what worked against your opponents. One tactic that helps is to have one bar set up with heals/defense so you can "turtle up" when your opponent is trying to dump a bunch of burst damage on you. Another option is to have yourself set up for "hit-and-run" and run instead of turtling up.

Damage
Its kind of the reverse of the defensive basics above.
Are you aiming for burst damage or doing more sustained damage "pressure" on your opponent?
If you want burst, you'll want to pay attention to when your opponent "turtles up." That's not the time to hit them with everything you've got. Instead, you want to hit them when they are vulnerable, so you might have to wear them down with less costly attacks so you can get their guard down and then attack. If you do "hit-and-run" tactics, you can often get some players to spend their resources chasing you and then, as long as you aren't out of resources yourself, turn the tables on them.
If you want pressure, then you'll need to work out how to keep damaging your opponent, such as with constant hits, poisons, or bleed damage. Its important to be able to stay on your opponent, or else you'll just watch them heal up and reset the fight if you give them breathing room.

I hope that helps and you have a great time learning to PVP! Don't get discouraged with dying a lot. PVP has a steep learning curve and we've all been there. It gets better with practice!