It is not common to start showing at 5 weeks and 2 days of pregnancy. However, every woman's body is different, and some may show earlier than others due to factors such as muscle tone or previous pregnancies. While it is possible that you are carrying twins if you are showing so early, the only way to confirm this is through an ultrasound scan.
As for your symptoms of extreme fatigue, constant back pain, and breast soreness, these can be normal in early pregnancy. Fatigue is a common symptom due to hormonal changes and increased energy demands on your body. Back pain can occur as your body adjusts to the changes in your center of gravity caused by the growing uterus. Breast soreness is also a common symptom caused by hormonal fluctuations.
However, if these symptoms are significantly affecting your daily life or if you have any concerns about them, it's always best to consult with your healthcare provider. They can provide personalized advice based on your specific situation and offer guidance on managing these symptoms.
Remember that every pregnancy is unique, and what you experience may differ from others. If you have any concerns or questions throughout your pregnancy journey, don't hesitate to reach out to your healthcare provider for support and reassurance.