Frustrating yes. It's hard being pregnant, but I hate to say it, even after you hear that hearbeat you're still going to have days of wondering. You have 4 weeks in between appointments (at first) and a lot of worrying can happen if you let it! Try your best to think rational thoughts, I for one had trouble with this! ;), but it really will help you to be grounded. Also, I really liked the book My Pregnancy Week by Week as opposed to What to Expect... I felt it was a better way to present the material and it was easier to read. Plus, having something every week made me keep my craziness in check!
Everything is okay...and congrats!