First time pregnancy anxiety?

I just found out I am pregnant last week. From our calculations I'm maybe 5-6 weeks? And so we don't see the doctor until the end of the month. 
I took multiple OTC tests that all came back positive, and then went to a 24 hour doc in the box to get a blood text which came back positive, and she said the lines were as strong as they get.
I'm a LOT worried though because this is my first time and I'm so scared that something is going to go wrong!
I had a period about 2 weeks ago (or so I thought) but it was extremely abnormal, and I have been told that many have a period while they are pregnant still. 
I have also been spotting ever so slightly since that "period" until yesterday.
I've had the traditional sore breasts, gastrointestinal discomfort, and some nausea, but today everything seems to be not as bad! I have minimal soreness in my breasts, less cramping, no spotting, but I'm still nauseous off and on.
Why is my body changing so rapidly?! Could I have had a miscarriage and not even known about it?
 Am I freaking out over nothing?