I'm really sorry you are going through this too. I miscarried 10 days ago, for the 2nd time within 3 months, at 7 weeks. It was my 3rd m/c, and I too already have 2 children (aged 18 & 5) but the point is, if you have decided you'd like more, and gone through the whole process of planning, conceiving and then anticipating your new child, then of course it is going to hurt tremendously when you lose them.
I actually went to hospital each time. Am not sure if I should be "wasting" NHS resources when, as you say, it seems obvious what will happen but there are a couple of things to consider. Firstly, there are some women (albeit not many) who have had horrendously scary bleeding suggesting a m/c, but who have been found to have another explanation for the bleed and who have gone on to have a normal pregnancy. The hospital can obviously confirm this. Secondly, a scan will check if, after m/c, there are any "products of conception" (horrible term but I can't think what else to say) left which may or may not need medical intervention. I wanted to know that it was okay to try again, and wouldn't have wanted to worry that there was any slight risk of infection, further bleeding and/or pain if not everything had been passed. Plus, going to hospital also means you are in the system should any further investigations take place ... it's absolute proof that you have miscarried when you say you have and might just swing it for you if your doctor is otherwise reluctant to refer you for tests.
Having said that I've just been to see my GP who's referring me to the gynaecologist at the hospital in case there is any underlying reason (other than bad luck and my age - I am 44) for what's happened. He couldn't have been nicer about it and has also said that if I conceive again in the meantime, he will hurry up the referral and ask for me to be monitored more closely ..... for example, by checking to see if oestrogen treatment would help me to maintain the pregnancy.
I don't know how old you are but it might help you to feel more "in control" by seeking advice and help from your GP. Yes, we all know that the vast majority of m/cs can't be explained, but there are things that can be done for some women and personally I want to feel that I have done everything I could to help myself no matter what the outcome. The worst thing your GP could say would be no, but then you'd be no worse off.
How far along are you ? Had you seen the midwife yet ? ..... if so, give her a call ..... I expect she would suggest going to hospital (if you can, with 2 littlies) for similar reasons as the ones I've already mentioned.
Take care of yourself ...... this horrible "limbo" period, awaiting what is probably, sadly, "inevitable" is hell, with each trip to the loo a depressing and upsetting can't-believe-this-is-happening experience.
Remember you can always come on here to "talk".