If you are cent per cent sure that you never had sex, you may forget about the pregnancy
. Your delayed menses could be due to other hormonal dysfunction.
You are having voracious appetite and still you are thin and lean. This is suggesting the possibility of Thyroid dysfunction
. Please get your blood examined for T3, T4 and TSH.
Thyroid dysfunctions are common at this age; however they are more of low Thyroid function
in which there is loss of appetite and weight gain.
Please report to your Gynaecologist and get hormonal work up done. Then you may be started appropriate treatment.
Finally, delay in the menses just once should not alarm you. Keep a watch, if the irregularity recurs, you may start investigations with the advice of a Gynaecologist. Currently you may take some progesterone
preparation like Deviry for 5 days and you should get menses within 4-7 days.
I hope this helps you.
Dr. Nishikant Shrotri