As usual I can't give specific answers, only an idea to what might be happening...
AB's themselves don't drop blood glucose levels, but because they tackle the infection that can cause our blood glucose levels to rise, which give the impression that they can drop them!
I see that you started your AB's on Saturday and your dropped kicked in Monday, which just happens to be the point where AB's have built up enough to really start impacting on any infection...
So it may well may be that your drop is the AB's are doing it's job and clearing your infection.. Hopefully your drop will settle down now as you either finished or nearly finished your BG course, so it will spend the next few days just mopping up the last remnants of the infection..