Welcome to healthcare magic
Itching over the gluteal cleft is commonly due to fungal infection
. It could be candidiasis
or tinea. You seem to have some sort of pus discharge from anus. This itching could be due to irritation caused by the discharge as well.
It is better to get a dermatology consultation to diagnose your condition. Causes of anal discharge
could be sexually transmitted infections like gonorrhoea, chlamydia, anorectal fistula, abscess, external hemorrhoids, inflammatory bowel disease
is unlikely to cause it, but rarely a granulomatous lesion around anal orifice may cause discharge. A diagnosis can be made only if i can see it.
Hope this helped