I found nipple guards made the pain worse. It protected my nipples, yes, but DS had to suck so much harder to get the milk out that it felt like I was having boob liposuction. 
I remember that feeling of having shredded, bleeding nipples all to well, and of having to ball up my fists and curl my toes and sob though the pain just to get my babies fed, and I really, really feel for you.
In my experience there isn't always a solution or an answer, except to stop. People will tell you you must have the wrong position, or the baby must be tongue tied, or not latching on properly, try this, try that, do it hanging from the lampshade etc, and sometimes despite plenty of help and support to make sure you are doing right, you are still in the most unbelievable agony.
Sorry to be so negative but that's just my experience after trying to feed three babies and giving up after a month. 
Try everything you can, by all means, so long as you can stay sane throughout, and I genuinely hope you crack it and it all falls into place. But don't let anyone make you feel like a failure if one day you just cannot take it any more and reach for a bottle of formula. You'll feel guilty enough by yourself without inviting anyone else to heap on the shit. If you decide to stop, make your decision, stand by it, never look back, and never apologise. It's a wonderful thing, but it's really not the be all and end all.