Will antibiotics affect my period?

Hi!
I'm on antibiotics (penicillin) until the 30th August (been on them since Wednesday so it's a 10 day course) for a nasty bacterial infection in my sinuses. I'm on the pill, but just recently I've been getting spotting whenever I go to the toilet. I know antibiotics affect the pill, but is this a sign that my period is going to get messed up? I'm going on holiday in about 2 weeks so if it came on time then it would be perfect, but if not, I'm going to be on my period on my holiday!
I was just wondering if it's known to affect my cycle and whether I'll come on early or late? Or totally on time? I'm due a week on Wednesday so not long anyway. It's better that I come on late than early though! Is the spotting anything to worry about or is this normal on antibiotics? I am around the time where I would spot if I was going to spot.

Thanks!