You know, I was just talking to another mom at my daughter's ballet class the other day and we discussed the same issue - how we both noticed that body odor seemed way worse after our kids were born (I have 2 kids, this other mom has 3 kids). I actually think that it has something to do with stress hormones, because I have noticed in the past couple of weeks now that my work has become extremely stressful, that my deodorant isn't working as well as it did. When you think about it, your life is pretty stressful - you just had baby #3 and you are going through a divorce. If that isn't stressful, I don't know what is! I have also noticed with both of my daughters, even though they are young, that they tend to get body odor when they are really stressed out (exams at school, that kind of thing).
As far as a brand recommendation, the clinical strength ones seem to work best, but they are kind of pricey. I have used the Degree clinical strength kind and it worked really well.
Best of luck with everything! Congrats on your new baby!