I can't swear your situation (since I'm allergic to penicillin and never take it), but I have, in the past, taken probiotics while being on antibiotics. It's the only way I can keep from having diarrhea while being on them. Some people have heard that probiotics diminish the impact of the antibiotics, and that you should wait until after you're done with the antibiotics to take the probiotics, but I read about a study in which people in hospitals were given probiotics while being on antibiotic regimens to see if it reduced their antibiotic-associated diarrhea during and after treatment (it did). Some people recommend you take your antibiotic at one time of day and your probiotic at another to keep them from battling against each other, but the new antiobitics that are out now (that I've been put on) get into your system and work for like a week after you stop taking them, so I don't think taking your probiotics at any particular time helps or hinders in any way, since they're long-acting antibiotics anyways.
My rule of thumb is to take probiotics either right before bed (because they make me gassy), or to take them when I take my antibiotic just so I'll remember to take them. That would be my advice to you.