This is very unusual and odd occurrence. When I developed that pain almost I immediately connected it to my hemorrhoids. I had some mild pain every now and then after bowel movements and got used to it. But pain after coughing was new symptom for me.
A cream I used for hemorrhoids didn't help me, so I concluded that it must be something else. A friend of mine told me exactly the same thing, that anus pain can be caused by certain antibiotics.