The sperm transmission from the ductus deferens to the urethra during the orgasm is via the EJACULATORY DUCTS which lies within the PROSTATE GLAND. So the answer to your question is YES, prostate problems can be one of the causes of weak ejaculation.
You need to determine if your main concern is just about weak ejaculation or possibly there is LESS VOLUME OF EJACULATE. If the volume of ejaculate is less, then of course the ejaculation will be weak. You need to do semen analysis if your ejaculate is less than 1 ml (normal is 1.5 - 5 ml). Low volume ejaculate can be caused by low androgen levels, retrograde ejaculation, structural obstruction, or frequent ejaculation (as in fequent masturbation).
The main function of the prostate during sexual activity is on ejaculation. Any abnormality in the ability to ejaculate should not be mistaken as problem in erection. Erection mainly depends on the blood and nerve supply. And yes, smoking and alcohol has some impacts on blood circulation and have some negative effects on erection.
This link has good information that may be helpful to give more details to answer your questions: http://www.vitroman.com/prostate_problems.pdf
Thankyou for your reply.
I think that I may have an enlarged prostate,and I will seek help from my doctor.Could an enlarged prostate (consideringwhere it's situated) cause me to feel that I need to empty my bowels more even when I cannot go any more,causing me to sit longer and strain,hense bringing on the symptems of piles.Could it be a sort of viscious circle? This feeling in the anus makes me worried about the medical examination.
I look forward to your reply