I nursed my second exclusively and got pregnant around 4 months (hadn't had a period). Once I found out I was pregnant, I realized that's why my baby wasn't wanting to nurse as much. It does change the flavor of your milk which bothers some babies, and some it doesn't. I had to start supplementing formula because he just didn't want to nurse. I kept nursing as long as I could and eventually it was only during nighttimes (he didn't care to reject it because he was so sleepy). At 8 months he started sleeping through the night and that was the end of breastfeeding. I gave birth to a healthy little boy 5 months later. (My oldest was 2 when the 3rd was born. So I had 2, 1, newborn - all boys. Let me tell you - that was hard! But 2 years later, I can honestly say I would do it again. My boys play so well together and just love each other. With 2, 3, 5 years old, I love having them so close.
Yes, it was overwhelming to think about, but just like all babies, the days go slow and the years go fast. Enjoy your time with your babies! (Best you can on 0 sleep :)