Congratulations!
I remember being in the same position as you 15 weeks ago. We got our BFP and, instead of the crazy, excited jumping about that I imagined there would be it was more of a cautious daze.
I went to the doc the very next day and she was fairly disinterested and told me to make and apt for my first antenatal appointment for 8 weeks. This is called the 'booking in' appointment and takes about an hour. It's mainly filling in A LOT of forms but also you'll have your blood taken. I had to choose the hospital I wanted to give birth at (which seemed ridiculous at this point as I hardly felt pregnant!)
Your next appointment will be the 12 week scan (woooo!) where it all becomes real. And that's it for the first trimester.
I'm not going to lie, it's a difficult time. You're kind of left to your own devices and the wait until 12 weeks is painfully slow. I paid for a private scan at 8 weeks as I was convinced nothing was there. It cost £80 and was honestly the best £80 I've ever spent. It have me a milestone to focus on that was nearer than the 12 weeks. And once theyd seen the heart beating they told me I had a 98% chance of continuing with a successful pregnancy. I was still as nervous as anything about the 12 week scan but it broke the time up.
I think you've got the right attitude about being cautiously excited but just remember you chances of a successful pregnancy far outweigh the opposite. It will be the slowest 8 weeks of your life and you will be knicker watching constantly. If you feel ill just see it as a good sign that all is going well. If you feel fine (as I did!) DO NOT panic. So many people don't actually suffer from morning sickness at all.
You will also probably get cramps (although again, maybe not!) but don't panic about that either. It's your little bean nestling in for the duration.
Just get yourself busy and stay distracted because otherwise you'll go mad thinking about it. Take each day as it comes and each day will mean odds of a successful pregnancy go up and up and up.
Good luck! Exciting times!!
(it goes quicker after the 12 week scan, although it's still scary - Im 5 days away from my 20 week scan now and soooooo nervous, eeeek!)