The problem is that by doing the tests, you're looking for reassurance/confirmation. Which is fair enough, because This is an extremely stressful time. There's no way to know everything is OK, and for those of us who've miscarried, that possibility is so very real. I get it, I really do. I had a different issue I was constantly seeking reassurance for.
BUT, doing tests does not reassure you, does it? Because you have seen that they're still positive, and you're not reassured. And paradoxically, doing tests, seeking that reassurance, then not getting it, or only being reassured for a short time, actually makes things worse. You don't get reassurance so you keep testing (in my case I kept asking. I drove everyone mad but I was so desperate to be reassured that I was OK). And the more you test, the more anxious you get. Therefore the more tests you do. It's a horrible, vicious cycle.
The thing is that nobody can tell you what will happen with this pregnancy. You might miscarry, you might not. Scans won't tell you, nor will pregnancy tests. Scans only tell you what is happening at that exact moment. And even if you feel reassured by a scan, the nature of this is that the worry will shift to another, slightly different focus.
But you can feel better. You have to be strict with yourself. You have to recognise your anxious thoughts for what they are, and not get consumed by them. You have to stop seeking reassurance (ie testing) because it keeps the issue in your mind, it stays present, and becomes bigger and bigger. Testing makes it all worse. So even though it is SO hard (and I do know how hard it is) you have to resist the urge to. The more you resist the urge, slowly the better you will feel. It's a very similar issue to health anxiety, with the same kind of thoughts, so any advice for health anxiety should help you here.
Good luck OP 