Hi,
Welcome to HCM.
Rectal pain or anal pain on left side radiating to your knee could be indicative of piles,fissure or some
anal infection but the other uncommon causes must be ruled out like large bowel obstruction,
ulcerative colitis,intussuception etc.
You may require thoroughly clinical examination,routine blood counts,stool tests with proctoscopy and
colonoscopy to rule out any other lower GIT etiologies.
You may require below mentioned drugs for which you may need to see some local surgeon who will know about it.
1) Antibiotics (quinolones like ofloxacin or norfloxacin with antiprotozoals like
metronidazole or ornidazole) with,
2) Topical application of steroids with lignociane creams or ointments to reduce pain and inflammation with,
3) Hot sitz bath,
4) Laxatives or purgatives to have a soft and effortless stool evacuation.
5) Vitamin b complex with folic acid to have a rapid healing of ulcer if there is fissure.
Consult general surgeon who will your take complete medical history and clinical examination with relevant investigations to detect the underlying cause.
Hope this will help you.
Regards,