Due Date

I had a miscarriage and got pregnant again before my first period. ? I'm not sure how far along I am though. I think I'm about 6 weeks but I'm really not sure. I have my first appointment on August 9th. Will the doctor be able to give me a due date then or tell me how far along I am? If this has happened to you I'd love some insight. I've had three consecutive miscarriages so I hope this baby sticks!