I am taking both right now and at the same time.
I don't notice ill effects but felt like my heart was pounding a couple of nights. I Googled that and some people have issues with Bactrim like that.
I noticed I was less tired when I forgot one day to take the Bactrim also.
I have no stomach issues so far really but one person advised waiting maybe an hour to take the second antibiotic if you have issues.