I'm glad your midwife was able to offer some support and reassurance, LST, though I know it's still frightening. Hang in there.
Hopefully it will stop soon or if not, you will have a scan and will then know what's happening.
To add to what teaandflapjacks says, my spotting has been going on for a week and sounds much the same. I was scanned on Thursday (routine scan which was already booked because it is an IVF pregnancy) and as at Thursday little bean was OK despite the ongoing spotting. My GP will refer me for a scan at the EPU if the bleeding worsens, just like your midwife said to you, but will also send me for another scan if I am still spotting a week after the last scan, to check if everything is still OK because a scan is obviously just a snapshot in time. Can you ask your midwife if she will send you for a scan if the brown spotting continues for more than a few days, even if it,s got no worse? I'm sure they will and it might be reassuring to know that's what will happen and you won't be left in limbo.
It might also be reassuring to you that a possible cause of spotting which my GP and clinic have both mentioned, apparently quite common in early pregnancy because our hormones are all over the place, is cervical erosion ie bleeding from the cervix. This would not harm the baby. My GP has said she will examine my cervix if the spotting continues, in case it's just that. Has your midwife mentioned this possibility? A friend spotted from 6 until 14 weeks from her cervix and the baby is now a healthy 8 year old.
I won't say don't worry because you are bound to, and staying positive is hard, but try to distract yourself first of all with something routine at work if concentrating is hard. Do you have a work friend you trust who you could confide in and will hold your hand when you get low at work?