My girlfriend doesn't have period for two months

My girlfriend doesn't have her period for two months and she's complaining that her head hurts (a lot) 

Untill now she hasn't been complaining about anything else so I don't know what's happening... Her period wasn't something you could count because it is always irregular. Last period she had (back in January 12 I think) She barely bled. Only a few drops... One time she told me that she hadn't have her period for 4 months so I don't know what's going on... 

Take a pregnancy test

Get her to take a blood test for pregnancy. Best results and 110% accurate