For some women fertility while BFing comes back with AF but for lots it doesn't. My friend ttc while BF for 11 months and finally got PG 3 weeks after she weaned, even though AF had been coming all that time, her body just didn't sign up for PG until the milk bar was shut.

You have had a baby pretty recently and your body has been recovering. Imagine you'd had that scan a month later - you'd have been PG and the subseptate uterus would have been a by-the-by observation, since you were already pregnant. If it caused no worries the fisrt time i wouldn't anticipate any next time. If you ttc for 7 months after DD is completely weaned and nothing happens, THEN it might be a sign of something.

Bx