Eh, most of the time I think the campfires are well-spaced. Make sure you're burning your shards to give yourself more Estus Flasks, those are key. Also you can allocate your faith pots to regular health pots at the blacksmith if you aren't a magic character.
I am pretty new to the series and it's definitely a struggle but it's about managing your health. You can't afford to take damage vs. every foe you face, so you have to learn the ins and outs of each opponent. Most aren't that difficult.
As an example, there's a mob that looks like a butcher, he has a giant hacksaw. The first time I fought him I had to use 4 estus flasks (health pots) just to kill him. Now I can take him out without taking any damage.
It's definitely frustrating, but not unfair, and the reward for learning how to easily take apart a mob that used to own you is really awesome. As opposed to many games that favor button mashing and just overwhelming your opponent, DS3 teaches you how to gauge distance, when to block, when to tumble the out of the way, and when to react very quickly when your opponent starts to wind up. You're going to die, a lot, but by the time you get to around level 40, you're rolling around and blocking a ton of attacks with your shield and immediately responding to the threat. It feels very weighty, like an actual swordfight should. Get lazy or sloppy and a lot of enemies can rip you to shreds. And it changes based on what weapon you have. If I know I'm going up against short ranged fast enemies, I switch over to my greatsword, because I can hit them with a lot more range and keep several of them at bay with one swing. Completely shifts my strategy vs using an axe, which can typically only hit one enemy at a time.
Worst case, if you're really struggling with an area, you can just summon a friendly spirit to help you. What feels impossible by yourself becomes very manageable with 2 or 3 people in your game who can take some hits for you and stab the dude in the back when he goes to finish you off.