15No Period? No Relaxation.
Do yourself a favor and don’t try to track your period as a means for preventing pregnancy. Ovulation, the actual egg dropping, can happen in as little as 25 days after a woman gives birth, but there won’t be any period for at least 2 weeks after (completely hidden) ovulation.
What this means is that you can get pregnant again within weeks of giving birth without having even one period, or realizing that you were back to your monthly cycle.
Besides which, you have just had a massive hormone dump. Your body will be struggling to get back to a routine, with other factors delaying or speeding up the return of ovulation. This can make predicting your fertility like predicting the weather - not something you want to bet on. If you want a break between pregnancies, you will have to put your plan in place immediately.