Me and my other half are trying to conceive. due to type 1 diabetes and reoccurring infections he has to take co-amoxiclav which is 500mg amoxicillin and 125mg clavulanic acid. how will this effect his sperm?

Shouldn’t affect the sperm at all, but to be certain may want to check with fertility specialist or have motility study done on sperm

The issue here is whether the medication lowers testosterone or raises estrogen levels in the male. Both of these effects could impair male fertility. As suggested a fertility expert or perhaps the pharmacist may have this information. Since you're trying hard to conceive, it's worth checking further.