I am a 2IFer, wrapping up my 2WW tomorrow, but I think you'll be happy to hear what I have to say regarding your nausea.
Three days after ET for IVF#1, the same thing happened to me. We were out to dinner with a huge group of friends for a birthday celebration, and I got sick, twice, then was fine. Our friends all knew we were doing IVF and said "you're pregnant!" I told them, and meant it, that it was too early and just a coincidence.
Well, as luck would have it, two days later I got my BFP, and 9 months later, had DD. I mentioned the situation to my RE and told her I figured it had to be a coincidence. She said it was very likely the first big surge of HCG after implantation.
So, I say to you, be cautiously optimistic that this is a sign of pregnancy. Try not to stress out if you don't get a BFP right away. I got mine at 5dp5dt last time, and this time, it was 6pd5dt (I'm not counting this as definite yet though, because I also had some brown blood with it, waiting on beta first). The nausea is a good sign that the HCG is in your system, but it will take some time for enough of it to be there to show up on HPT.
Good luck to you, it sounds very promising, if not very pleasant!