The pill takes a couple of days to get out of your system anyway, and seems as you started taking antibiotics on the wed and the doctor gave you the morning after pill I would say that there is not much cahnce that you could be pregnant.
But as you will be taking antibiotics for at least a week you should use extra contraception for that time as antibiotics affect the pill working properly. Or just don't have sex for a while (thts a bit borning tho).
If you have any doubts then I would just do a pregnancy test, but I'm sure you will be fine if you just play it safe for a while until you are better.