Also, is he teething? The ammonia in pee gets a lot more concentrated when bubs are teething. But also second the strip wash

We use Use about ¼ cup of cheap washing up detergent, to strip ours. Hot wash, maximum 60deg and rinse until the bubbles are gone. Ive heard some of the PUL doesnt like the vinegar (I think its the PUL?) anyway its worked great for us
And also (Im not sure if you are doing this already) but generally you only need half the amount of laundry detergent that you would use if it was a clothes load