Why does your penis get hard?

Most likely your penis gets hard when you want sex or need to do something with it. The penis gets filled with blood when you get sexually aroused so you can perform intercourse. For most men, it often gets erect first thing in the morning. That has to do with the sleep cycle and the need to urinate.

If you are living with your parents and suspect you have a problem with your penis, you would want to ask your dad, not your mom. Otherwise, if you are an adult, you should ask a doctor.