DNA test

So baby daddy wanted a DNA test because he was doubting baby was his all of sudden, his ex found out about baby then he just wanted a DNA test we did one and it’s come back negative. I slept with someone on the 3rd of April 2022 we used a condom and the second time we did but he didn’t finish and I’d literally just stop taking the pill this was after having a period on the 15th of march 2022 I then had a period on the 12th of April. I then slept with baby’s daddy about 4 times towards the end of April after my period. We didn’t use anything and I’d come off the pill completely. I tested at the start of may and got a negative so tested again after my period was due on the 10th of may 2022 very faint line I didn’t notice so tested again on the 14th of may 1-2 weeks pregnant. All the scans add up to the date I would have conceived etc. so how the hell is it negative and he ain’t the dad? I watched him swab and we posted it together?