I would go with waxing if you can, but if that's not an option the only thing I can think of is to make sure you're moisturizing enough. Like maybe use a bit of baby oil and take a warm washcloth to the area beforehand or sit in a bath first. Definitely use shave-gel, a new razor, and try to avoid going over the same area more than once with the razor. Then re-moisturize well with a high-quality after-shave lotion <-- go for something fragrance free. Of all the lotions I've ever tried (which is a lot because I'm a total product whore!), Kiehl's 'creme de corps' is the best, and works especially well for this sensitive area too.
If none of that regimen works for you, it sounds like you just have really stubborn hair. It might be worth a few waxes just to get things settled - the hair grows in finer too when you wax.
Dancing-Doll is right, waxing works great. My wife and I both get waxed. No razor burns! A whole lot of me is as smooth as a baby's butt! Including my butt!
As other people have said before, you should really try waxing! yeah it is paintfull but really worth it!! and as DD said hairs starr growing thinner and the skin feels so much better for way longer!!
Right now im doing the (electrical waxing??? no idea how to say it in english) and im loving it!! it doesnt hurt at all and it will be permanent, the only down side is that it is expensive!
Make sure your razor is sharp and new... old blades tend to cut skin as well, leaving you with very small cuts.
I'm too chicken to wax, I just trim really well and shave the exposed areas. As a model, they will go psycho if they see any hint of hair popping out of a bikini! zIs laser hair removal painful?