Is it bad not to have your period when on the IUD?

So i have had my IUD in for about 19 months and haven't had my period for about 9 months of that 18 months. Recently i have had some strange side effects. Tender Breasts, extreme tiredness, head aches, spasms through my body, and crankiness.(i do have a doctor appt. tomorrow) I am just curious what happens when you don't have your period. Women have their periods for a reason so what happens when it stops...can that be bad and hurt your body? I have had a daughter she is 21 months. (I no that not having your period is a side effect of the IUD)