What Causes A Delayed Period, Cramping, Nausea And Exhaustion?

sir, i have stoped using femilon for 10 months, my period was regular but nw i got period after 5 days of my expected day. geting cramp & feeling exahausted also get nausea feeling but pregnancy test is negative when checked. what is the possibility? am i pregnant? is it a side effect of familon that the period is delayed?