I can't answer your question but over treatment used to be a problem. You're asking Is yours under-treatment. After a biopsy and an MRI there isn't much more to do. Do you know how many pins the biopsy used and how many had bad cells?
Your prostate seems large as well which might be why your psa is high.
There's often a worry between psa tests even when you've been treated. You're in that position, although six months gap is quite a while at this stage I'd think. Three months could be more normal but there must be a minimum period after your biopsy which was in January which makes 6 months gap seem reasonable, since your October biopsy.
It looks like you will have to hang on and establish a psa trend with 3 monthly tests from April. Unless someone knows a case to have earlier psa test. Regards Peter