Hello Sir,
I just read your query. The most common reason behind the
rectal bleeding is hemorrhoids(generally called as piles) and
fissure in ano.
Constipation is the common cause behind both of them. Sometimes unfortunate causes like ano
rectal cancer may cause bleeding too.
* As your doctor have ruled out the hemorrhoids. In hemorehoids the veins of
rectum and anus are swollen and inflammed. Hemorrhoids can be dry or with bleeding.
*As you told that you get bleeding only after drinking then the probable cause may be
dehydration. As drinking may lead to dehydration in the body and dehydration may further lead to constipation. In constipation hard stool occurs which may lead to bleeding fron rectum. Sometimes you might not face other symptoms like pain, itching etc. but only get bleeding in stool.
* The mass you have seen through mirror may be the swollen veins which are visible after straining or after putting pressure. It can be polyp but can not be ruled out without clinical examination.
* You have made a right decision to visit your physician. As only with the help of local examination doctor will rule out whether that are swollen veins or anything else. If that was swollen veins and its only hemorrhoids then he will provide you treatment and diet modification according to that. But as your are worried about cancer, and if he finds something wrong then he will definitely advice you some investigations and you will come to know about your exact cause of bleeding.
* Till than avoid taking alcohol and spicy food and excessive caffeinated drinks.
* I hope you are satisfied with my answer.
Thank you.