As far as the blood and soreness in the rectum area, this may be hemorrhoid related or anal fissure (tear in the rectum area) You can try to get a mirror to see which it may be. Which changes in BM can occur after being on antibiotics.
Below are two excellent sites that explain about Hemorrhoids as well and additional information on what can cause them along with treatment and prevention. read here
read here
The arm and fingers you describe sound as though this may be related to a nerve. Which could be pinched or entrapped. If this is something that doesn't go away in about a week, you should follow back up with your doctor, as you may need an NCV and/or EMG test can indicate where this is occurring for proper treatment. If left untreated could cause further damage.
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