While or Merina it is common to have periods which can become irregular, heavy bleeding and spotting between periods. These are more common during the first 3 top 6 months. After a particular period of time your body adjusts and periods become lighter.3 weeks is a too long time to have continuous bleeding. Too much of blood loss can result in weakness,dizziness,syncope and shock.Nausea,sore breasts, mood changes are also few of the side effects seen while on Merina.Consult a gynecologist and get yourself checked. Do keep me posted.
Best wishes and regards!