Have you tried experimenting with cock rings? There are quite a few different sizes and shapes.

I note you are 22 years old. My answer would not be relevant to your situation. I have been in a committed, exclusive, relationship with my wife for over 50 years. Through the years as our bodies have aged we have adjusted and refined our sex life to accommodate these changes. One of the major adjus...

For some reason I am imagining going to sleep with a pump on and rolling over in the middle of the night and whacking my wife in the tush with it.
Very likely I would have NO need for a penis pump ever again!!

Why is the specialist recommending a pump? If it is for exercise/rehab purposes then there is probably no need to shell out 100 or more dollars. A good medical grade pump, while costing more, can be used for both penetrative sex and for exercise. My experience has been the medical grade pumps are a ...

All I have is a low cost sex shop pump. I have had many low cost pumps through the years. They are great for exercise and for the low investment. To get and keep an erection for penetrative sex I have had to use restriction rings and for that purpose I have had to invest in medical grade pumps. Tha...

What is your goal with this pump? Low cost sex shop pumps are fine for exercise. To get and keep a firm erection with a vacuum pump you would need a medical grade pump. For help with your pump follow the link below, scroll down to vacuum erection devices and click on the link under "How to Use ...

In my Army days I had so much more on my mind that my dick size. I don't recall ever thinking about it back then. But that was over 50 years ago and time has made those days kind of hazy.

I'm sure he means a medical grade VED

I use an Encore deluxe. Cost was $125 us dollars and was the best $125 I have ever spent.
Some medical supply stores can give you an idea of what is available. Here's one of many.
https://www.vitalitymedical.com/penis-pump.html

I'm with bldoink on those pumps. For what purpose is your doctor recommending a VED/VCD? If your doctor wants you to use the pump with a constriction ring, then a medical grade VED is called for. If the purpose is more for exercise and to help blood flow and not use a constriction ring, then the pum...

I don't think you can "gain" beyond the limits of your genetics.