Does anyone else have irregular periods?

So I'm 17, I've had a period since between my 7th and 8th grade summer. I've always kind of had irregular periods. But here recently, for three months in a row my period came on time. Which was the months March, April and May. Then the summer came around and I haven't had my period since. I am sexually active. I've taken a pregnancy test which said negative. Is this normal?