I'm so sorry for your three miscarriages.
I've had three PGs and three miscarriages at 20, 7 and 11 weeks.
It does feel very unfair, you are right.
I don't have any answers in my case as all the tests came back inconclusive, as others have mentioned, but I would think that the fact that you have carried a baby to full term, albeit with a difficult pregnancy, suggests things are much more positive for you in terms of your chances in future, although i'm sure it doesn't feel like that at the moment
I found lesley regans book 'miscarriage' very helpful (she is in charge of the recurrent miscarriage clinic at st mary's in london, one of the best in the world) as it goes through all the possible tests and problems that may be behind the mc's.
As for whether to wait or not, I was told after all 3 of mine to wait until i'd had my first period as it then helps dating the next PG, (which can be important if you are having early reassurance scans to check things are OK and you are less far along than you think at the scan it can cause unnecessary anxiety).
Several nurses, docs etc have also suggested waiting for three months afterwards, but when i have questioned them on this there is no science behind it, it is to 'emotionally recover' so i've felt free to completely ignore it as I have always strongly felt that it is important for me to deal with things in the way that is right for me.
There is no getting round the fact that having your hopes dashed like this three times is shit, and dealing with the physical aspects of MC is also shit. Be gentle and kind to yourself if you possibly can, its a horrible, horrible thing for anyone to go through.
I wish you every success next time and pray we both end up with late 2013 babies.