Chris you should take a great deal of encouragement that your treatment, that has reduced your PSA from 114 to undetectable in 6 months, has been an overwhelming success.
You completed RT in April 2020, your PSA nadir should be 18 months after RT finishes so on this basis you're in the clear until October 2021 at least.
You shouldn't worry about your next 4 tests although admittedly its not easy not to.