COULD I BE???

I had my DD in July of 2016 and my period came back in December 2016 and I've around 28-29 days ever since. My husband and I had unprotected sex 7 times ranging from the start of the month to the end. Yesterday I was 4 days late and I took a test and it was neguative. Could my cycle just have messed up or I ovulated late? Could I still be pregnant and when should I check?