Weak erection and constant pressure

Somebody please help. I have this problem for 4-5 years now and I am 28. I have constant pressure and discomfort in the penis and I keep having to pee because of it. I feel like urine is stuck or there is some stinging feeling in the penis from the tip to may be around 1 inch down. Sometimes I also feel pressure behind the testicles. My erection is always weak and short and it only gets erect with touch. As soon as I start masturbating or having intercourse I feel like I need to pee because there is so much stinging feeling in the penis so I just ejaculate. When I ejaculate or pee it feels like there is no force or strength just like I feel there is no strength in my penis. Please help me I am going to go under depression because of this. I got the bladder ultrasound done and it was fine.

change your diet try eating clean that helps