Jody,
It's more likely the cyclosporine, not transfused blood, that is producing this side effect. Read the
Cyclosporine and shower issues thread by another mom. You can post there too if you'd like to compare notes.
After ATG, patients usually need to stay on cyclosporine for many months, with 6 months to a year being typical (every case is different since it depends on the patient's rate of recovery). However, doctors usually reduce the cyclosporine dose over that time, tapering gradually. Trevor's cyclosporine side effects should lessen as the dose lessens. If they don't think there's a real danger they probably aren't going to want to reduce his cyclosporine simply because of side effects. That's because it would increase the risk of an VSAA relapse.
It's very good that you are gathering information for Trevor since he doesn't have access to an aplastic anemia specialist. Despite the unusual circumstances it sounds like he's gotten the correct treatment so far. ATG and cyclosporine is the standard approach because it has a good success rate.
If you haven't already gotten it, order the free booklet
Your Guide to Understanding Aplastic Anemia from the Aplastic Anemia & MDS International Foundation. You, Trevor, and his hematologist should all know that help and expertise are available just for the asking.