Hi purple
I'm really sorry for your loss. This is a very supportive place to be if you want TTC again, so make yourself at home.
As AandRmum said the pregnancyloss site has invaluable advice,
this page really spells out WHY the doctors as you to wait.
My case is a horrible scary example of why waiting can sometimes (although rarely) be very very important. I had a mmc, followed by medical management but not all tissue came away. I keep spotting and stopping and bleeding for 2 months, a couple of times I thought I had my period but it turned out later not to be. I had lots of clear scans and then later during one scan it was found that placental cells had regrown and I was diagnosed with partial molar pregnancy. This is really rare but very serious and needs to be treated with chemotherapy. I had an ERPC and the tissue was analysed and in the end I got the all clear, it wasnt molar. BUT if I had got pregnant in this time I would have definitely had another mc and been at risk of developing cancer. (Also, in these cases, even after treatment you have to wait 6 months to a year before being allowed to TTC again)
So, the bottom line is, if you wait for AF you know for sure that the mc is over, there are no complications and you are good to go as it were.
The dating thing will be more of a problem for YOU than the doctors. If you get pregnant again soon and go for an early scan (which you will want for reassurance) they might tell you the baby looks "small for dates" i.e. not growing, and that you will have to wait for your 12 week scan to confirm this. The doctors will happily send you home, and leave you to deal with this all by yourself. It is therefore a good idea to know as best you can when you conceived so the measurements can be interpreted accurately.
The absolutely bible concerning all things fertility related is the book Taking Charge of Your Fertility by Toni Weschler, it will teach you all about charting, etc) Also very good is the free site www.fertilityfriend.com which has tutorials with the same sort of info.
You should definitely wait until a HPT says you are "not pregnant" otherwise you wont know if a positive pregnancy test is from the end of mc or if you are newly pregnant. Do you now what the results of your blood tests were? If you had a quantative HCG test this can give you an idea of how much longer it will take before the pregnancy hormones leave your system.
Lastly, if you are thinking about using OPK's (and HPT's) I would check out Amazon, there is a substantial price difference as opposed to what you get in the chemists.
Oh dear, I have written a novel 
Will catch up with everyone later, much love! xxxx