I know exactly what you mean, I experience the same thing. To help out, I do exercises almost every day where I stand in front of my bathroom mirror and try to get an erection without using my hands.
I do the same without hands while sitting down. It’s a really good way to get accustomed to getting an erection through mental stimulation. Not to mention, almost every time I’m in my truck driving down the road, I unzip my pants and pull my dick out to let it get erect. It’s a great way to keep the tissues stretched out and pliable. I just have to be quick to put my dick back in my shorts when truck drivers or large SUV’s pass by, because they could look over into my truck and see me sitting there with my dick out lol!