I've had similar grazes following falling off a bike, on elbow and hip. If it is weeping, one of the 'faster healing' gel type plasters stuck on for a few days will stop it drying out and cracking. The area around it will be bruised, hence the pain. An ice pack may help, and also with the red puffiness. Arnica (cream or tablet) is one 'homeopathic' solution that apparently has some basis in reality, for reducing bruising. But you must make sure it is really clean. A dressing may help stop clothing sticking to it, if nothing else!