Hi,
Welcome to Health Care magic

You need not worry. Delay in periods is common after using I pill. The periods may be delayed by 2 days to 2 weeks in some cases. As it has been 3 days passed by from her expected periods date, I would suggest you to wait for 3 more days before coming to a conclusion.

And about the pain abdomen and Head ache -these could be premenstrual symptoms. Women often experience pain abdomen and headache 1-2 days before menstruation. Or it could be even due to gastritis.

If you still have a doubt you can perform an Urine Pregnancy test kit at home. Negative result suggests that she is not pregnant.

Wish you a healthy life

Take care bye

Thanks for the query
As mentioned by you that your gf took i-pill , now let me tell you something about this drug , i-Pill consists of one 1.5 mg levonorgestrel pill & this pill is indicated for the prevention of pregnancy after an act of unprotected sexual intercourse . This drug has been very common among the teenager's now days but lack of knowledge regarding this drug is extremely harmful . plz know some facts about this drug
1. Nausea, vomiting, lower abdominal pain, a feeling of breast tenderness and headache are some common side effects after taking i-pill but these usually subsides within 24 Hrs of administration of drug
2. unexpected vaginal bleeding, but this is not dangerous and it should clear up by the time of the next period
3. i-pill might also cause the next period to come early or later than normal whats expected on routine .
4. Frequent use of this drug can cause ovarian damage and menstrual problems, especially among younger girls
5. Last but not the least - Continuous use may reduce the chances of future pregnancy.

Now all this was to make you aware of the drug you are using , now as far as your problem is concerned . Kindly do UPT ( urine Pregnancy Test ) at your home only as these kits are availible at any Medicine Store nearby . If it comes positive you can plan accordingly , as far as in your case normally during periods or just day or two before usually girls show these symptoms of pain in abdomen , headache's etc etc . So go ahead do a pregnancy test and USG Scan if necessary if all these dosn't help do consult a GYN/OBG doctor