Get your blood test to rule out cancer, but then, see a chiropractor, you symptoms are probably due to pulled muscles or misaligned vertebrae in the lower back area, that is why the NSAID gel is helping.
I would suggest you make an appointment to see your doctor.
The doctor will examine you at his surgery and will be able to feel if you do have an enlarged prostate. Other signs of an enlarged prostate are having problems to urinate. You will have an urge to urinate but will have difficulty in peeing. Frequent urges to wanting to urinate could indicate a urinary infection.
Checking for prostate cancer would involve having a blood test to begin with.
Don't worry about it, but book that appointment and get checked out. If there is any problem, the sooner you get treatment the better.
Best wishes.