Lower back pain after ejaculation.

I had taken one yr alpha blocker like alfuzosin and in between before 10 silodal 4mg due to slow urine flow. Now, I have stopped taking this medicines from 15 days and 1.one of the problem which i saw was related to ejaculation is that after masterbating i feel little burning inside penis or 2-3 times i have to urinate after masterbating.  2.2nd thing which i saw was that the speed of ejaculation or semen speed coming out has decreased. 3.So can there be low sperm production due to this medicines for life time  or can this medicine affect permenantly to prostate or any ejaculation issue for life long? 4.Also, I feel sudden lower back pain after masterbating just once, and then fatigue whole day and i feel weakness after erection. Now i used to masterbate everyday, and now with one masterbating i am having this problem. So, my question is what is this problem that I am having and should i wait for 15-20days to be back to normal or this can be lifelong due to this Alfoo alphablocker???