My first thought would be, how are night feedings going? My period came back at 4 months, and my daughter started sleeping through the night at 3 months. With my second, it came back at 6 or 7 months, and my son never really did sleep through the night until 10 months. Sometimes night feeding can affect it.
Other than that, I'd say don't worry about it. Having a period come back at 6 weeks is actually a little on the shorter side of normal, I'd say. I don't want to say it's abnormal, because I don't know what the exact range for average is. But just as with babies' development, there is a big range of normal for women and postpartum first periods. I know women who don't get one until after their baby is a year--whether they nurse at night or not. It all depends on the woman.
So I'd say, rejoice that you don't need pads yet. It will start soon enough!