I think you can go for a urine pregnancy
test again with the morning urine sample,if negative go for a sonography
, to know if there is any other cause for delayed periods. there are chances of pregnancy as you have missed a few pills.
Consult your doctor with the reports, i dont think antibiotics have any effect on your menstrual cycle,delayed periods might just be due to hormonal
imbalance or stress
Don't worry, take care