when should i let my doctor know i am pregnant

I took a test Saturday morning and it said I was 3+ weeks so Im guessing that means I could be 4 or 5 weeks pregnant ???? this will be my second baby but since giving birth last year I've had problems since with pooing ect so I've had loads of appointments a camera up my bum ect to try see what's wrong with me but they haven't so I have another appointment in February to see a specialist again so thought maybe If I tell them they could push it forward? thanks in advance.