After I Went To The Toilet On Monday - 3

After I went to the toilet on Monday - 3 days ago - I got a severe pain in my left lower abdomen. I had to strain as the stool was very hard and very, very large. So large it would not flush. Anyway since then the left abdominal area is very tender to touch and the pain only comes when I move or breathe. I am taking ibuprofen but the pain is getting worse. I would be grateful for your thoughts and potential diagnosis.