Thanks for providing more information.
Sorry for late reply and inconvenience.
Firstly as you have rectal bleeding,pain during defecation so it indicate the possibility of Hemorrhoids,Anal fissure,Colon polyp.
Constipation can be main culprit for your rectal bleeding.
So you need to discuss it with your family doctor as sometimes augmentin can increase your rectal bleeding and cause other GI symptoms like Diarrhea/loose stools nausea, vomiting, abdominal pain or cramps however not so common.
You should start metamucil and start probiotics if you want to take Augmentin.
Usually antibiotics should be given to prevent secondary infection during dental work.
So it is good to take antibiotics for 3-5 days before your dental work.
And you can ask your dentist for other antibiotics like Metronidazole which is not known to cause rectal bleeding and can be safe for you.
Now for your constipation you should start fibre rich diet and avoid spicy,fried food,alcohol.
Further ano-rectal examination and colonoscopy should be advised in your case.
Hope this helps.
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