As mentioned, the 'balnket' rule is 'testing after three' (and even then, I think sometimes you need to be a bit proactive and ask before anything is done...).
But, as also mentioned, there certainly are sympathetic GP's/consultants who are willing to bend the rules in some circumstances.
For instance, I'm five weeks out from a mmc at almost 17 weeks. The baby delivered in a clot the size of a bowling ball, absolutely unbelievably massive... and as it seems logical to me my uterus filled with blood for this to happen, I asked my GP if the blood would also have ended up in my tubes and in turn would this mean they are blocked or would the clots eventually get reabsorbed. She said that they wouldn't necessarily get filled with blood but if they did it would be reabsorbed eventually, however, if I came to ttc and nothing was happening after a couple of months (she knows I get pregnant just by looking at my partner...) then she was happy to start some testing 'even though we don't usually - you've been through such a traumatic experience' (and I'm reasonably 'mature' at 37).
I don't know how I feel about ttc right now but the fact I know that if it comes to it, my gp is behind me rather than shoo-ing me away with 'you were just unlucky' is so reassuring.
Do you have a good relationship with your GP? If not, could you foster one? I know what you mean about it being hard not become obsessed (especially when we have other little ones to consider) so perhaps a visit to the GP is in order just to talk about that aspect - I think it's reasonable that most GP's would recognise our mental health can certainly be soothed by actively treating something that is physically a huge issue in our lives. Long term physical pain is known to cause depression, why not mental anguish too? However, if you don't voice your feelings to your GP they'll never know it's a problem for you, y'know?
So sorry for your losses, I really hope you can continue on to a healthy pregnancy soon.