Maintaining erections or you are not able to sustain the erections, that is also Erectile Dysfunction. For ED issue there are Physical and psychological reasons. First you need to consult a sexologist and tell him your proper case history, then he can guide you properly. Even some time counseling also can resolve the issue of ED due to anxiety performance. If necessary I can advise you some medicine , that will be without side effects.

<!--td {border: 1px solid #ccc;}br {mso-data-placement:same-cell;}-->The problem is known as erectile dysfunction... It may seem concerning but it is curable..your problem of erectile dysfunction most commonly occur in ages of men: fortunately it has high recovery rate of 90% through ayurvedic medications. 

I am explaining briefly about erectile dysfunction so that it takes fear out of you. 

In erectile dysfunction, men are not able to get or keep an erection that is sufficient to have penetrative sex. This may be due to so many factors like High cholesterol, High blood pressure, Diabetes, excessive masturbation, excessive Porn watching, nerves weakness, Obesity, thyroid, heart problem, alcohol, Tobacco use, Sleep disorders. Low testosterone, tension, stress etc., 

This problem of erectile dysfunction is very much treatable. 

I am suggesting you some ayurvedic medicines, 
Take Aswagandhadi churan half teaspoon in the morning & in the night. 

Take Capsule SHILAJIT One in the morning and one in the night. 

Take tablet Brihat Bangeshwar ras one in the morning one and one in the night after food. 

All three preferably with hot milk or with water 

Also apply and message Shri Gopal tail on your penis three times a week for 2 to 4 minutes. 

Avoid junk food, oily and more spicy food, alcohol, tobacco, tension and anxiety. 

Start doing brisk walk or running or cardio exercises for at least 1 hour a day. 

Start taking hot milk twice a day also two to three dates in the morning and in the night with milk. 

Do all the above suggested treatment for 3 months and see the results. 

If you don't get satisfactory results then please go to your family doctor or a good sexologist.