Do I need a dna test?

I had sex with an ex on the 15th Nov 2023. The rest of the days I had sex with my current partner. I believe I conceived with my current partner on the week after I had sex with my ex due to stretchy cervical mucus, ovulation pains and so on. I tested 2 weeks after the 15th nov and the test was negative. I tested positive on the 5th of December. Is the baby most likely my current partners or could there be a chance it’s my ex’s. I suppose not? As I didn’t get a positive pregnancy test till the 5th etc..

Just thinking about the odds in getting a dna test done.

I had my scan on the 30th Jan and was dated 11 weeks and 3 days.

My question is that if it is my exs, how come I didn’t get a positive test 2 weeks after sex. I tested on 1st December and it was a negative

Also the scan done on 30th January was an nhs scan which they include the two weeks before conception so surely the dates aren’t too close as as it would be the 29th nov where I conceived as I add 2 weeks from the 15th nov and that’s when my conception date is?? 29th nov