My theory is that because I use a condom the feeling decrease consequently causing me to lose some of my erection.
When I am not wearing a condom and she is giving me oral it seems to be great, but once we move on to intercourse I put on a condom and little by little it begins to decrease until it reaches semi-hard.
Is there anyway I can maintain an erection for a longer period of time while using condoms. Will doing physical exercise increase my erection? And finally, should I resort to pills to increase blood flow?
Fantastic questions. Yes, condoms do decrease sensation. And you can use that to your advantage. You could end up lasting longer, having more time to bring her to climax before you go.
Now to help you enjoy the condom more. I learned a little trick about putting on a condom so that sex later would feel better. I put a little lube in the inside tip of the condom before puting the condom on. This way, the lube allows the head of my penis to be stimulated by the movement of the tip of the condom. It does add sensation for me.
Before you resort to pills, ask yourself some serious questions like: Do I have high blood pressure? Do I have heart disease? Do I have diabetes? If any of these conditions exist, you should see a doctor about wanting better erections because there are many options available surrounding these conditions. Now, if you are a young guy and this has nothing to do with a physical condition where the blood flow is somehow interrupted to your penis, I would suggest getting professional sex counseling around it. Perhaps you have feelings about using the condom that go beyond the loss of sensation. Perhaps you have some anxiety around needing to wear a condom in the first place. Perhaps you have some anxiety about being able to perform with a condom. A professional sex counselor or therapist would help you sort through those things.
And all of this could be done together... Examining physical causes and examining emotional/psychological causes. We have to remember, especially with sex, that our minds, emotions, spirits, and bodies are all connected. Sometimes an erectile issue lies more in the emotional/mental/spiritual side of things even though it looks like it should be handled by physical means because it's a physical problem. I sincerely believe that being honest that sex is where most of us learn that mind, body, and spirit are connected and we share these parts of ourselves with our partners. There is an energy exchange here (and sometimes even a fluid exchange) and things should be in balance for it all to work.
Best wishes, and relax. It's just sex....