Oh my darling, Sparkly 
I'm so angry that this is happening to you again. Please ask to see the fertility specialist. Tell them you have had two chemicals and that the GP is unhelpful because the surgery HPT doesn't pick up the pregnancy. I don't think a fertility specialist will disregard your BFPs simply because you test before AF. Sparkly, what you need are progesterone suppositories. I was ordered to take Utrogestan progesterone suppositories (400mg per day) by my IVF clinic until the twelfth week of pregnancy, when the placenta takes over progesterone support. This is not a harmful product. It can not do any damage - even to a pregnant woman who doesn't need it. I would never recklessly advise someone to buy prescription meds online unless, like this product, it is harmless.
You need prog support, Sparkly, but I feel you will keep getting knocked back unless you can 'prove' your pregnancies in the GP surgery - and of course you can't do that when you are miscarrying within hours of getting a positive on an HcG. Your embryos are surely coming away with the shedding of your uterus. I don't know why your charts are healthy when you are losing blood days before your period is due, but if the nurse tomorrow does sweet FA to further some investigations which would lead to progesterone support I would fuck her off and order these 
P.s...2 x 200mg suppositories a day up the vagina (one in the morning and one at night) supports vulnerable pregnancies like yours. Even if prog deficiency is not your miscarrying issue, these suppositories will do no harm...it is simply progesterone and nothing else.