Ultrasounds can be off by up to a week. They're not 100% accurate..
If your second partner took off his condom and you guys still had sex, there's a chance he could have gotten you pregnant.. even if he didn't ejaculate inside you... pre c u m still contains sperm...
So honestly, there's a chance it could be eithers...
a dna test after baby is born is the only way to be sure...
Sperm can live up to 5 days 7 if it's a healthy environment. The only way you could be 100% positive since its so close together would be a DNA test. Everyone makes mistakes.
Dna test is the only for sure way..
Ultrasounds aren't accurate to the day, they could be off by up to a week at that point in the pregnancy. There really is no way to know other than through a DNA test.
Sperm can live up 7days in the uterus. So even if you didn't have sex on the 16th it still could be the living sperm from the 14th and 15th.! I would say its the boyfriends. But ultimately a DNA test is the only 100% way to know who is exactly the father!
This makes it very hard to figure it out.
Your best bet in my opinion is to wait until your baby is a little bigger and if your local hospital has the correct equipment have them do a DNA test.
They can do it while the baby is in the womb still.
My mom had to do it for me when she was pregnant. (My dad was in denial.)