What are the causes of erectile dysfunction?

Hello doctor,

I would like to ask for your opinion regarding my erectile dysfunction problem. In high school, I did not have this problem, frequently having strong morning erections and responding to external stimuli like kissing, touching, etc. Before college, I had a car accident with no genital pain, only back pain (not sure if it is relevant). After the accident, my morning erections become weaker and shorter, around 10 to 15 seconds instead of two to three minutes as I was used to. During college, I noticed that I responded less to external stimuli. When interacting with girls, I had weak erections, and I could no longer achieve an erection without touching. The issue worsened when I noticed that my right testicle is softer, smaller, and more descended than the left. I concluded that it was the cause. I went for a check-up, and the urologist said the problem was psychological, not testicular (I felt treated superficially). I did tests and a scrotal ultrasound, which were normal. Another factor might be that I was overweight, eating unhealthy, and had an erratic sleep schedule. Since the beginning of the year, I started going to the gym, eating healthy, having a regular sleep schedule, and taking supplements. I noticed psychological improvements (reduced anxiety and increased confidence), but the ED remained. I rarely have morning erections, and they are weak. Recently, during an interaction with a girl, although I was stimulated by kissing, I could not achieve a strong erection. Currently, I can only achieve an erection through masturbation. I know that in the absence of sexual activity, the degree of ED cannot be accurately assessed, but the anxiety that I cannot perform during sexual intercourse prevents me from taking the next step. Kindly help.

Thank you.