I am not sure if I is really the antibiotic or the reason you are taking the antibiotic. but being sick and changes in routine as well as stress can all make us irregular with our period and delay it. So, I'd say it's all related. good luck hon
In the last 3 months I've taken 3 different types of antibiotics for mastitis, I usually start the 14 but started my cycle today a week later... I don't believe it's a serious issue, but it definitely happened to me.