Hello Tarun Rana and thanks for the query
Your girlfriend is getting regular periods after may, so their is no chance of being pregnant. So don't worry and feel free. On thing I want to tell you that if a female is pregnant than she did't get her menses at all till the baby is delivered .
As she misses periods in may, it could be due to some other reasons like stress
, illness, change in schedule, being overweight
or being underweight
. Needs to be investigated for this. Consult your doctor for this.