Why am I not able to maintain an erection?

Low libido has a wide range of causes and rarely one single explanation. Physical contributors include low testosterone, thyroid disorders, raised prolactin, diabetes, sleep deprivation and obstructive sleep apnoea, chronic illness, and a long list of medications — SSRIs are among the most common and most under-discussed. Psychological and relational contributors matter at least as much: depression, anxiety, stress, relationship difficulty, and — relevant here — the strain of trying to conceive itself. Scheduled intercourse over months can turn sex into an obligation, which reliably reduces desire in both partners. Worth checking: morning testosterone (levels vary through the day, so timing matters), thyroid function, prolactin, blood sugar, and a review of current medications. If you are trying to conceive and sex has become a task, that is worth naming rather than pushing through. Reducing the intensity of timing — regular sex across the fertile window rather than precisely scheduled — often helps more than any treatment. See a doctor if this is persistent or came with other symptoms such as fatigue or mood change.