Could Mood Swings And Irritation Be Due To Contraceptive Pills?

My girlfriend started taking the combined pill around 5 weeks ago, for the past week she has been acting very distant and seems to be very irritable. She doesn t talk to anyone as much as she used to and seems overall, less happier. However she also has exams coming up in 2 months time which could be a parting factor. She claims she s happy with the relationship and doesn t want to leave me, so i doubt it s linked to that. Do you think her acting distant and her irritability could be due to the pill?