Hi, Thanks for your query, After three negative pregnancy test , chances of pregnancy are very less. However confirmation may be done by serum bhcg or ultrasound. Breast feeding may also cause this type of irregularity of menstruation or even amenorrhea . Pregnancy is also less likely because the hormone required to stimulate milk production prevents the release of the hormone that triggers ovulation. Pregnancy cannot occur if an egg is not released. Take care and best of luck. Hope it helps..