delayed menstruation

First time mom po ako. Ive been breastfeeding for 1 year napo. When i gave birth after 6 weeks nag mens din regularly,monthly. Except this may to july. Wala po talaga ko mens. Kala ko im preggy , i tested, its negative pregtest. Dahil po kaya to sa breastfeeding? Or baka need ko na mag pa Ob ulit?. Or tlgang may chances mag irreg pag breastfeeding? Thank you mga mommies sana may ma advise po kayo thank you