You've had too many ultrasounds too early. I'm not a huge believer that ultrasound use is that safe especially so early when the baby is first forming and I just cannot understand why you've had four ultrasounds before six weeks.
Honestly, with a tilted uterus, there is still a good chance you will not see anything. I know it is hard but you may want to consider waiting a week or two to have that ultrasound. I was not able to see my baby until almost nine weeks.
And, yes, a tilted uterus does matter. We've seen it too many times to know that it does. One thing to keep in mind, though, just because you have a tilted uterus, does not mean this is not a miscarriage, just makes your chances of misdiagnosis a bit higher. But, as early as you are, there are many women with and without a tilted uterus who cannot see their babies yet.
I'm a little concerned about this doctor you are seeing. YOu might want to consider a new doctor.