Hi
My situation was very similar to you. We had been TTC for 4 years when I fell pregnant with my DS. I didn't even find out I was pregnant until 9 weeks (we ended up concieving naturally) because I had no symptoms at all and gave birth to a healthy baby at 39 weeks. I was also very paranoid because of how long it took us to concieve but like others have said all pregnancies are different. With my DD I was sick almost from the moment they did the transfer. If you are worried ring your doctor and have a chat. Mine was always very helpful when I had a concern.
Nae is also correct about the placenta taking over at the 10-12 week mark. Because my DD was IVF I stopped taking all the hormone medications at 12 weeks because that is when the placenta begins to support the baby, so that could be a reason the symptoms have lessened.
I hope this has been of some help and Congratulations on your pregnancy!!
Monica