Your doctor has put you on Primolut depot to protect your pregnancy. You had a little spotting of blood which could be due to some risk of abortion to your pregnancy. Primolut depot is a progesterone preparation. Progesterone is a hormone which is required for maintenance of pregnancy. If doctor feels that your body has lower levels of Progesterone, he/she will start some medicines to increase your levels of progesterone. This progesterone has an effect of water retention in breasts and make them heavier and tender. As it is during pregnancy, the size of breast increase, they start secreting milk and thus become heavier and tender. So you need not attribute your breast symptoms to Primolute Depot. Heaviness and tenderness in the breasts is a good sign in pregnancy. You may have to change the size of your brassieres and buy new larger size ones to accommodate your enlarged breasts comfortably and support them. That proper support to the breasts will give you some relief from your breast symptoms. Please do not take any pain killers for the breast discomfort.