This is definitely a problem that you should talk with your doctor about. Most of the time, trouble with sexual function is treated by your primary care doctor, although some cases may be referred to a urologist as needed. There are many things that could cause trouble to achieve a firm or sustained erection. Your doctor will want to take a full medical history and perform a complete examination. By far, the most common cause of erectile dysfunction is stress, fatigue, or other psychological factors. However, prior to attributing the issue to these factors, it is important to rule out another medical cause. For example, there are several medical diseases that are very commonly associated with erectile dysfunction. These include diabetes, heart disease, obesity, and various hormone deficiencies. Furthermore, various common prescription medications may cause erectile dysfunction, including medications that are used to treat high blood pressure and depression. After your first visit, your primary care doctor will determine whether you need additional testing, such as blood tests, to look for any of these different causes. They can also help you determine whether the erectile dysfunction is significant enough that it should be treated.