With my first I was deathly ill for the first 3 mo, and with this set of twins I have also been very sick, but with my second daughter I had zero symptoms... I only gained 8 lbs the whole time and she is perfectly healthy! I don't know how or why they can be so different but they definitely can be!
I had no symptoms my first 4 weeks besides cyst pain on my ovary... But sounds like youre lucky maybe with the 4th one! i wouldnt worry sooner or later you will begin all over again with the morning sickness ect lol
It sounds like you're concerned this may not be a healthy pregnancy.
This is kind of a wait and see situation - it does sound like it might not be a viable pregnancy, but it certainly could be.
Best wishes.
I had no symtoms with either of my first two pregnancies. They resulted in two beautiful girls. Don't worry. Every pregnancy is different.