Nervous

So am super excited to find out that am 5 weeks today. Long story short we had been trying to get pregnant for over a 1 1/2 year so we went to the doctor to find out if I was able to get pregnant to our surprise we where pregnant our Christmas present we find out Dec 22 on my brother birthday but I told my 15 year old son on Christmas Day. So why am I super nervous will January 1, 2017 my first child will be 16 years old in two years he will be 18 going off to college. Am I crazy to be starting all over? I will be 34 in 2017. Will I have the patience? For one baby let alone twins. My boyfriend wants twins.