Do me a favor and read this older post just to rule out if it could be this:
http://www.redearslider.com/forum/viewtopic.php?t=1590
Also here's what the main site says about prolapse:
Prolapse
The appearance of a turtle's intestinal, usually colon and/or reproductive organs, through the cloaca (the opening on the underside of the tail) is a prolapse. Ingested gravel or some other impaction may cause this situation but may not necessarily be a factor. If the male merely exposes his reproductive organ, then it's referred as "fanning" and is not a prolapse. In any case, the organs return to their normal position and there should be no cause of concern. If the organs cannot retract, then that turtle should be isolated immediately. Soaking a turtle in clean, warm water might help correct the situation. However, if it does not or if the organ(s) has been bitten, injured or scratched by another turtle, then a vet visit is immediately required. The area must kept clean and wet until proper medical attention is given.
And one more thing, a herp vet is just a vet that does specialize in reptiles/turtles. The stickies at the top of this section will help you be able to locate one. Here's the link in the US:
http://www.redearslider.com/forum/viewtopic.php?t=370