Smelly Diapers

Recently my son's urine has been really smelly and now his diapers are starting to keep the smell no matter what we do. We've added extra rinses (2), tried more detergent, tried less detergent, changed him more frequently, washed the washing machine twice. I'm not really sure what else we could try, we air dry and the smell is pretty obvious while drying too. I'm trying to figure out why my son's urine is smelling but is there anything I can do in the mean time to get the diapers to smell better while his urine still stinks? They're clean and poo smells aren't sticking around just urine smells, I'm just at a complete loss. Been using for a year and never had this happen before.