Hi Welcome to HEALTHCARE MAGIC..
I have gone through your query and can understand your concern...
Yes delayed periods along with
abdominal bloating & back pain could be caused by pregnancy if you had un-protected sex in past month. Pregnancy causes hormonal levels of progesterone to rise which could give rise to symptoms such as nausea, abdominal bloating, vomiting,
morning sickness etc.
You should first get a pregnancy test done to be sure you are pregnant or not. Pregnancy test is easy & could be done at home by using a home pregnancy test kit. Follow instructions on pack. However there are other reasons that may cause delayed periods such as
1. Hormonal disturbance such as
hypothyroidism could cause delayed periods
2.
Excessive weight gain or weight loss can delay your period.
3.
Eating disorder or high exercising in last month could also delay your period
4. Excessive stress (even related to getting pregnant) could also delay your menstruation by hormonal change
Refer to a gynaecologist
Hope this information helps