What are the side effects of antibiotics Amoxicillin 500mg and Clavulanate 125mg and will it affect your period if you are given a week's dosage on the second day of your period?

They don't affect your cycle as much as they affect your birth control pills----they block them. You must finish the antibiotics and then take ACTIVE pills for 7 days before having sex without a backup method like condoms. Also, you really should not get medical information like this from Answers.com. For something this important you should at least call planned parenthood to talk to a doctor.