I highly doubt you have an infection, so be careful about being on antibiotics long term.
I still have that rectal pressure 10 months out, but it's definitely improved somewhat.
I think that the pain causes you to tense your pelvic floor, or the pelvic floor muscles are in spasm due to nerve damage.
Deep breathing, relaxation techniques and pelvic floor relaxation exercises/stretches are key here. I didn't start doing that until 4 months post-vas and I wish I started right away. They've helped a lot and I don't feel like I'm sitting on a tennis ball anymore.
Where are you located? You're still early and might be totally fine, but you should get your ducks in a row and find a good PVPS doc. The asshat vasectomist who did this to you will probably tell you it's not PVPS, just an infection or prostatitis.
Good luck to you.