I find that very interesting as well. I have found that I tend to get anal itching every now and then and have successfully used hydrocortisone cream to relieve it and eventually it goes away. Have you tried any treatment or cream.
Also, repeated scratching of the anus and lower butt crack area only serves to make it worse, so the sooner you get some cream the better.
I do find it curious though, that after you poop you cannot get sufficiently clean, even with wet wipes, so I agree with illustriously fickle that you should get checked out.
Hope this helps,
Wendy