Thanks for writing in to us.
I have gone through your query in detail.
As you have mentioned , you are 28 weeks right now.
is actually dated by the last menstrual period, but since you do not remember that, it is dated by the first ultrasound
Luckily you had an early ultrasound in the first trimester itself, at 7 wk 5 days.
Based on that ultrasound, the conception would have occurred around 20th XXXXXXX and not by the episode you mentioned on 5th XXXXXXX
Also, as you are reasonably certain that no seminal fluid entered the vagina at that time, ,please be reassured.
By such tremendous guilt, panic and worry, you will be putting your health and the baby's health at risk.
Think positive, and enjoy the blessings of motherhood and pregnancy.
Your due date - 29th March, also tallies with this ultrasound and dating.
I could not make out from the query - have you already gone for a DNA test ?
If so, you will soon be reassured, because if you had conceived on 5th XXXXXXX the date would have been atleast 2 weeks early, that is around 12th March, not 29th March,
And on 15th august, the baby would have been around around 10 weeks 1 day.
So please do not worry and take care.
The baby is in all probabiliy, your husband's.
Feel free to ask for further clarifications.
All the best.