Go to the doctor. they will give you an HCG test, give you all the info on pregnancy and answer any questions you have. You may also get a referral for a 6 week scan. I have my 6 week scan tomorrow.
I am like you, with my first pregnancy I didn't find out until 15 weeks too. But that was about 9 years ago.
I felt funny one day and went to the doctor for them to tell me I was pregnant! I had been seen 3 weeks prior (RIGHT after my period ended) for abdominal pains and they said I had a golfball sized cyst on my ovary. that I needed to come back in three weeks for a check up. I told her I was nauseated and that's when she gave me the news!! I was 2 1-2 to 3 weeks pregnant .. next week ill be six months.. it all depends on your body! They can do an internal ultrasound and see the baby or at least the sack this early! Good luck! And cuz of your so early labor. with your baby and the previous miscarriage just tell your doctor and they will be able to be cardio with you so nothing happened again.