I think everyone is different when it comes to symtoms and some will be worse than others. This is my third pregnancy and my symtoms with nausea left me fast I still have the sore breast from time to time , but I believe that is normal. My first and second pregnancy I was sick forever with nausea and I don't think I had sore breast for long ...but like i say pregnancies seem to vary. I think your one of the very fortunate ones to have symtoms leave fast I would not worry much at all. I too first saw doctor @ around 8 weeks and then started testing from then on. Congrats on your pregnancy and enjoy yourself as much a possible hun!
Same thing happened to me at 9 weeks and I freaked out! I'm 18weeks 2 days now and so far so good! So hang in there and try not to stress out.( I know easier said then done.)....Oh, and the breast soreness came back, the other stuff stayed gone.
Its really normal for symptoms to come and go. And lucky you if you only wind up having them the first 7 weeks! If it eases your mind, give your dr. a call. They can always test your beta/hcg's which, as far as I know, is the biggest indicator at this stage that all is well. Good luck to you, and congrats on your pregnancy.