Toddler is hysterical in the shower. Desperately need help!

I'm a stay at home mum to a three years old. He used to love taking baths and showers. So much he would undress himself and take a shower on his own or full up a bath for himself, sometimes as much as five times a day. Then suddenly it changed to the complete opposite. I don't remember exactly when it happened, but it wasn't roo long ago, say a bit more than a month ago. He gets absolutely hysterical, screaming and crying as if I would have tried to kill him. Not tantrum-crying, genuine fear and panic. It's like he is traumatised. However, I'm the only one giving him showers, and due to corona and my husband (who is his dad) works away for periods of time, so I'm the only one who had been with him. So nothing had happened to him to cause this.

I have myself been in threraphy for phobias, so I know how to work with it. However, I can't just stop having him the showers and baths until it's solved, like you'd build up with baby steps when treating most phobias. Our pediatrician can't help us, and I don't think theraphy would work as he is almost non-verbal and doesn't understand a lot (no underlying diagnosis, he was born premature, they think that is why he has been a bit "slow" with everything).

What I do now is that I tell him we need to shower and we go in and I do it as quickly as possible while holding him and telling him it's okay, I understand and it will be quick. I have also reduced it to as few times a week as possible. On the non showering days, I hold him and just stand in the shower with him for a few seconds and say positive things, like "it's okay, it's nothing scary, we'll just hug each other" and he will just cry "done, done, done" . He has no issues with the bathroom itself, just the shower, and we do a lot of water play etc without any issues. I have tried to have him wash my hair, but as soon as we get in the shower he starts crying. I have also tried to clean him outside the shower, as in a babytub in the kitchen and such, but nothing I can come up with makes it better.

It feels like I am abusing him by continuing to give him showers, even though I know I have to. I feel horrible. I desperately need help.