First of all, I am so sorry for your loss.
And as to your questions, when ttc after a loss there are a couple of thoughts about ttc right away. One is that most doctors will tell you to wait anywhere from 1-3 cycles. However, an increasing number of doctors are saying that you can try for another baby as soon as you are ready to-whether that be without a period or not. In most cases, there's no real reason to wait other than it makes dating the next pregnancy a bit easier as you have an LMP to use for getting an EDD.
So really, it's up to you. If a doctor gave specific instructions to wait, then it may be advisable to hold off depending on the reasons but if you had a fully natural miscarriage and your tests have gone negative, then as long as you feel okay with ttc right away, then you can probably go for it.
Just know that not everyone cycles normally after a loss. Some women are anovulatory until their first post-loss AF shows up, some women have incredibly long cycles as they won't start a new cycle until their hormones drop low enough, and some have cycle changes-heavier periods for a while, slightly longer cycles, etc. And some will go back to their usual AF right away. There's really no way to know what will happen until it happens.
Personally, I find it takes around 2-3 weeks for my hpts to go bfn again and AF usually shows up 4-5 weeks after that. And I tend to be anovulatory for at least one cycle but not always.
I hope this helps.