It sounds like performance anxiety and it's very common.
It's a vicious cycle, because if you're nervous about performing well, then you probably won't perform well. This leads to more anxiety, which leads to even worse performance, which leads to....you get the idea.
It's important to break this cycle and turn it around. Even though there might be no physical issue, it could be a good idea to try a pharmaceutical drug like Viagra or something similar. This can restore confidence. More confidence, better performance, better performance, more confidence, etc...
There are also natural herbal sex enhancers that can work too, if not quite as dramatically as a pharmaceutical drug. One positive is that you don't need to go to a doctor and get a prescription.
I know someone who tried an herbal enhancer and it said it helped him get over his performance anxiety. Maybe it was a placebo effect, I don't know.
Another benefit is that since he started using it he hasn't gotten sick. This was about a year ago. Anyway, if you're interested, the product he used is called Endowmax.