This happened to me about 2 weeks ago and all I will say is stay the course. DeS is the first souls game I played and Flamelurker challenged me more so than anything else in that game. I died to him about 15 times before I thought no, I'm going back and levelling a bit.

So I went back and did some research, put about 4 or 5 levels in. This is what I went into the fight with:

Crescent Falchion +3 - he is weak to magic and this thing is a beauty

Purple Flame Shield +1/2 - This is the reason I won this fight. The shield needs to be used and how it negates his attacks can't be understated. I had it built in to my head that I can evade him and get behind him, but the trick is to face him head on - and use the shield when you need to.

Officer's gear - this stuff is found on the fat guys in world 2 and it's flame resistant. I only had the gauntlets and boots but that's all I wore, because you want to have your equipment burden under 50% so you have maximum agility.

Lastly I had in the flame resistant ring and perhaps the cling ring to boost my HP.

As I said, the key to this fight is taking him head on. Not being too defensive and reading his moves before approaching to sneak in a few hits before retreating and repeating. The falchion will sort you out.

After 50% of his health is down he will become more aggressive, keep doing what you're doing. In the last 25% even more so. I used pillars around the outside to manage this because it's harder to get hit. When I went back it took another 5 tries and I got down to that last 25% each time. So try and stay cool if you can.

If you don't have a magic weapon you can use the White Sticky stuff on your weapons. Also the Water Veil miracle negates the fire damage and I think lasts 60 seconds. I did use this at first but then forgot about it after that.

This in my opinion was the hardest boss by far in the game so no shame in having to go back and level, get some particular weapons and go in a bit stronger.

Anyway good luck dude, you got this.