When a pregnancy test shows dark lines immediately after taking it, it usually indicates a high level of hCG hormone in your urine. This hormone is produced during pregnancy and is responsible for the positive result on the test. The fact that you are 5 weeks pregnant aligns with the positive result.
As for your abnormal period in January, it is possible that it was implantation bleeding rather than a regular period. Implantation bleeding occurs when the fertilized egg attaches itself to the uterine lining, causing light spotting or bleeding.
Regarding your concern about multiple pregnancies, while a darker line on a pregnancy test can sometimes suggest higher levels of hCG associated with multiples, it is not definitive proof. To confirm if you are carrying more than one baby, you should consult with your healthcare provider who can perform an ultrasound examination.
It's important to note that home pregnancy tests are generally accurate but can occasionally produce false positives or negatives. If you have any doubts or concerns about your test results or overall health during pregnancy, seeking medical advice from a healthcare professional is always recommended.