lower back pain on ejacualtion?

I'm in early (hopefully) stage PC - stats below.
For at least two years I've had radiating back pain on ejaculation and numbing of my pelvis when hiking or climbing stairs. I've assumed all along that this spinal problem contributed to problems and now perhaps to cancer. Anyone else with this experience?
And, with the cancer, I've read it can cause lower back pain.
I presume that would be well advanced but don't know, any thoughts?
In any case I am considering my treatment options now, leaning toward a natural path. I was already a vegetarian but ate milk products, way too much cheese and wine.
However, I couldn't afford co-pays for MRI or Genome testing so I don't know how aggressive it is. Accelerated jump with PSA last test. I'd love to think caused by dying cancer cells ;-)

63 yr old, 6ft, 190lbs.
PC diagnosed 12/2017. 16 core biopsies;
four had changes. mostly 3+3 and a little 3+4.
PSA 01/2009 3.05. 06/2017 9.5
11/2017 PSA 9.79 Free .62 %Free 6.33
03/2018 PSA 11.68 Free .85 %Free 7.28

I thought I had an advanced case myself for the same reasons. Then I learned it was arthritis. I knew I could get cancer at some point in my life. But I never thought I'd get arthritis. Only old people get arthritis.

tajwill,
So maybe you should go to another Doctor, a Medical Oncologist who give you better guidance and will get you started on Lupron or similar drug. Also maybe some medical assistance group could help you pay for that important MRI.
Of course, we are just laymen giving outlook only on personal experience with the PC beast.
Wings