Low sperm count

We did an at home test today and it was completely negative. The instructions (which I read after we collected the sample) said 3-7 days after previous ejaculation but we had sex Thursday so we are going to retest in 3-7 days. I can’t help but worry though. My husband is 44 and got tested 10 years ago with his ex and all was fine so I was feeling pretty confident. I’ve got 2 children with an ex but my husband doesn’t have any and I’d love to give him a baby. Anyone else experienced something similar? Thanks ☺️