Absent Periods

So from my 19th birthday which was on June 21st til October 21st I hadn't had my period. Between those time spans I took 4 pregnancy tests and all of them said negative. Then on October 23rd my period came on and is still on... Has anyone ever went through this? P.S. I was on birth control before this absence of my period and then stopped in April. Do you think that could have been a reason? Give advice please.