I don't know too much on lordosis in terms of treating it, but it is something you should go to a chiropractor or related fields for.

Gymnasts often have lordosis because of their posture (sticking out their chest), I myself have this to a certain degree I think. In either case, it would be best that you don't do weight bearing exercises on your lower back, or anything that puts considerable stress on it. What is occurring, in case you don't know, is that the spine's normal S shape curve has been hyperextended, if you were to lets say jump up and down it would put a downward pressure on it's already extended position and cause back pain.

Your major focus shouldn't be on orienting your spine around working out those abs, but fixing your posture and spine first just because you wouldn't want back pain for any physical activity you decide to do in the future, i.e. playing with your kids and picking them up.

Your pelvis may partially cause the lordosis, if you notice that you can somewhat rotate your hip forward and backward, which is hard to describe over the internet... Let me think of a way to explain this. Ok well, some people tend to stick out their butt a little more then necessary, if you rotate your hip inward, without moving your legs or your torso, you can slightly feel the angle difference as your butt moves inward and the angle between it and the lower back lessens. If you still can't visualize it, stand up and get to a mirror, stand to your side facing it, take both your hands, and with your thumb and index finger, have them touch both sides of your hip. (in the same direction as if you were to pinch the side of your hip) Now, without moving anything else, rotate your fingers on both your hands in any one direction, and rotate your hips accordingly as if your fingers were part of a machine that is causing your hip to rotate. Observe yourself in the mirror and notice the angle differences between your butt and your lower back. It may be a bit difficult to do so, as your hip has been in that posture for many years.

I will get back to you tonight and look at my old notes to see what that darn certification told me to do dealing with lordosis patients.

Thanks for the comments. I find that I can push my hip forward/backwards and I think my pelvis is tilted because when I look in a mirror wearing clothes the back of my jeans are higher than the front, if you know what I mean, so it looks as though my pelvis sort of dips downwards (on a side note: could this be a cause of painful sex?). I can pull my hips in too, so that my back is straighter, but as I said it takes a lot of effort and I can't hold it for too long, although this has got easier since I've been doing ab exercises.
Sometimes I can correct my posture and hold it comfortably for a limited period of time, but the main problem is when sitting down. I find I either slouch or hunch my shoulders, and I can sit up straight but I find it very uncomfortable and I have to sit on the edge of the chair to do it. I'm thinking of seeing a chiropractor when/if I can afford it. As I said before I don't really experience any pain except when doing certain exercises, but I intend on doing more of these so I'd like to prevent it.