Why The Periods Are Missing?

hi my last period was on 9th march after i met with my husband,on 30th march and we used pull out method afterthat my period was due on 9th april but it came very less in amount in 3 days after that i uesed pull out method till 28th april and now today is 30th may but i did not get my period i took two pregnency test but negative and no preg symtoms, but i have too much lower back pain and pain in left side.