You aren't doing anything wrong! Are you on insulin yet? If so, what kind? I was diagnosed a little over 2 years ago but I've only been on insulin for about 7 months. I am very sensitive to it so even little doses ( maybe 2/3 units) can send my numbers all over especially depending what I have eaten and what kind of exercises I have done that day... Stay positive and ask a lot of questions!! No 2 diabetics are the same so what works for me may not work for you but talking and asking is a great start