Is there a chance my girlfriend is pregnant?

We have had unprotected sex a lot and recently in the past week she has been getting lots of bad headaches (she rarely gets headaches), she's been getting fevers a lot lately too, but during the day she seems like she has energy, but when it comes to evening/night she gets in pain from her stomach hurting and takes tylenol for the pain and then tries to sleep but im not sure if its her feeling tired or if she is trying to sleep off the pain. she hasnt had her period for awhile (she does have an irregular period, but the last time she had it was 5-6 months ago). She gets hungry but when there is food in front of her she gets kind of neglects to eat it and says its like the feeling when your sick and you dont feel hungry, but her stomach growls like she is hungry so i know she can eat. she has taken 2 pregnancy tests and both came out negative, but i still feel nervous like i did before, thanks in advance