Thanks for posting your query.
It is very common problem to get delayed period sometimes. It is not related to any infection.
It seems from your history that you are not taking any other medication and no any sexual activity, so the only reason remains is stress
. You might have had an acute episode of stress due to any reason. As stress can be one of the important cause of delayed period because it causes secretion of certain hormones which can modify your cycle and can delay your period even for more than 10 -15 days. so kindly reduce stress and relax yourself. You would be free in next few days of the period.
Have a wonderful month ahead.
Dr Sanjay K Kanodia