Chances of being pregnant?

Here are the facts: 1. I had a baby this last January. He is six months and i am breastfeeding exclusively. 2. I had my first period after baby a month ago. 3. I am 4 days late for expected second period. 4. We use condoms only. I cannot take birth control. A handful of times we have had fun before putting on the condom but he never finished without one and they have not broke. How likely that i might be pregnant? I'm scared because i had a c section not to mention other disasters this would create. I didn't tnink much of being late but now my co worker explained a bunch of things my brain got confused interpreting a staff email... is my baby brain back???????